In terms of platform in general, there's not much I could add to the post I wrote earlier, which was indirect comparison of Android and Maemo and I was quite strict pointing out lots of Maemo's pain points.
Shortly speaking, it's a no-brainer that Android's UI is exceptionally compelling, especially on as good hardware as Desire Z. It's unbelievably fast and responsive and it seems that uptime and number of opened apps in the background doesn't really make much difference. I was stunned to see this device being consistently fast and robust on each and every day of usage without rebooting.
Plus, there obviously is exceptionally easy to use Android Market with lots of excellent apps, very good web browser with Flash support (as in Maemo5), great cloud integration with various services etc etc etc. Simply great.
If I could name at least one thing that Android doesn't do that good as Maemo does, then it would definitely be multitasking. On N900 I could any number of apps and switch between them easily, especially with help of 3rd party apps like camkeyd. In Android it's a bit less convenient. Firstly, number of "recent apps" seems to be limited, secondly switching between them is not as quick and sometimes apps brought back forward seem to be restored into their "default" state. Definite plus on Maemo side in that aspect.
Maemo has root access and ssh daemon pretty much out of the box. Android pretty much doesn't, however it's not impossible. It just takes voiding your warranty and putting device to risk of bricking to gain full root access to the device. However, I need to put a bit of disclaimer here, as in fact process of rooting differs between various Android-powered devices and afaik mainly depends of manufacturer (HTC in my case) trying to lock power users out of options to set their devices free.
There's also a ssh daemon available on the Market (paid) which doesn't require rooting to work, so thankfully there is still ability to send files over ssh.
Nonetheless, as Nokia N900 is in fact miniature Linux box with wide open Debian'ish distro inside, Linux geeks will definitely appreciate lots of hidden perks (apt-get, for starters) that aren't really available in Android-powered device, or at least not within my knowledge.
Another point where I think Maemo wins. Cannot play avi files out of the box? Cannot play online streaming out of the box? Surely, there's an app for that, yet Maemo does better job in terms of codecs support.
I must also say that Nokia's idea of integrating instant and sms messaging into single application is absolutely great and Android unfortunately doesn't provide the same sort of experience. I don't event think there's an app for that...
Since I am the kind of user that cannot live without hardware qwerty keyboard, this aspect of hardware is particularly important to me. And to be honest, after using Desire Z for over a week I can say this for sure - N900's keyboard is just better. I don't mind slightly smaller and tightly laid out keys. There are few other aspects that make it just better: 1) key press "feeling", Desire's is a bit too shallow and doesn't have that good tactile feedback which makes me less confident while typing on it; 2) arrow (cursor) keys, which just aren't present in Desire so users are forced to use optical joypad to navigate through text (horrible); 3)
On the plus side, there are few convenience keys (like Menu, Search, Sym) and also there's an option to assign many useful shortcuts to applications through two dedicated shortcut keys or via Search+[key] combination. Nice.
Don't get me wrong, Desire's keyboard isn't that bad and most of these gripes are probably just a matter of getting used to. Nonetheless, for someone using N900 for over a year, switch to Desire is a step backwards in terms of hardware keyboard usability.
There's one more thing to note about keyboard and it's that famous "Z" hinge that replaces usual slider approach to open up hardware keyboard. The very first impression is going along the lines of "wow, that feels extremely fragile and... cheap". But guess what. After a week I stopped being bothered and in fact I quite like it! I guess that's another thing which requires a bit of adjustment over few days...
Screen and buttons
Desire Z features exceptionally sharp, bright and very sensitive capacitive panel. I am hugely impressed by its quality. Performing UI tasks with it is absolute pleasure, where even lightest touches are flawlessly registered. I even caught up myself touching N900's screen to lightly after using Desire Z for few days.
When it comes to touch sensitive buttons under the screen, I found no issues using them at all. These are nearly as sensitive as the screen itself and it very rarely takes more than one touch to recognize it.
5 Mpix camera and 720p video - it just cannot be bad, I was thinking. Surprise surprise, it is bad! Camera is one of the greatest disappointments of Desire Z in my eyes. Pictures look great on the device itself (thanks to the screen, I would presume) but on further inspection on computer monitor it turns out photos, especially those done in low light conditions, are blurry and have lots of grain. Exactly the opposite to the N900, where photos don't look good on the device but much better on computer screen.
720p video mode is also quite disappointing. It just records 1280x720 pixels video resolution but it doesn't mean high quality, unfortunately. Shame, as I was looking forward to get fairly decent (as for mobile device, of course) photo/video shooter in my pocket.
It's definitely hard to tell for sure after one week of use when I still abuse my new phone a bit too much by just playing with it or exploring various settings or apps. Nonetheless, I have an impression that battery performance is a bit better than N900's, yet with all online and wireless bells and whistles at least daily recharge session is a must.
I must admit that on the day when Santa took me by surprise with Desire Z I initially felt something like "oh, well... I don't think I am ready to make switch to Android just yet!". I was still "married" to my beloved N900 back then, even if that marriage was quite rough at times and featured lots of "quiet days". But once I tasted that forbidden fruit of Android eden, I quickly realised my marriage with N900 must be put into separation, at least for a while. Simply speaking, Desire Z with Android is a kind of device that is just fun to work with. There's no more waiting ages for applications to start or the UI to respond to my basic input. There's no more wondering whether rtcom-call-ui plunged somewhere deep into swap space so it won't be able to catch up in time for incoming call. There's no need for rebooting every 3-4 days to keep my own sanity... List of gripes against N900 and Maemo could go on and on, even if Android doesn't quite offer all the openness and flexibility as N900 does and which geeks just love (so I do). Who said that geeks don't appreciate decent user experience anyway? So while I keep using my new shiny Android-powered Desire Z, I can't wait to see what future brings and how Nokia learns its lesson...