I've got one; in fact, I was originally going to get a U700 but then I would've had to wait for 2 months to get it, so I opted for what was immediately available - hence the D900i.
Had no problems so far with it as far as the core functionality is concerned. Where processing power wrt to mobile apps are concerned, it's a bit of a let-down. So, I bought a 1G SD card and stored all my pics and vids on it in order to free available space; also regularly delete SMSes, and save only numbers that I use regularly to my phone - all others on the SIM.
If and when you do get one, just do things that'll optimise the use/functionality of it.
Oh, and as someone mentioned earlier, Java apps are a problem yes.