I would say that the phone itself is dependable, and works great. The battery life is also decent, given the phone (it gets me through the school/work day with reasonably-heavy-but-sporadic mixed usage (no calls), and would last well into the evening; I can't tell you exactly how long because I tend to use it a lot more in the evening, and thus stick back on the charger around dinner time just in case).

I think, as was already expressed, that you're more likely to be disappointed because it's so awesome that you expect it to be even more awesome. :P Also, as long as you can resist the temptation to try all the latest-and-greatest-but-still-in-alpha applications announced on the forums, it should be quite stable. I, however, cannot resist that temptation. As long as you don't add the Extras-devel catalogue, you should be safe. I've found Extras-testing to be fairly safe, too.
If you've had an N810, I think you'll be happy. I still <3 my N810, but my N900 makes it look like a toy.
To give you a few examples of how awesome it is:
- I've used it as my primary computer for almost a month when my desktop's motherboard was shot, and it was sufficient
- While attending a corporate event where I was expected to do a demo on an app that wasn't quite finished, I finished writing and testing the app on the phone itself, in the presentation room (well, okay, technically I used the phone as a remote to my friend's server, which did the heavy lifting, but still...)
- I have Wikipedia on my phone. Yes, all of it.