I've had the A900 for a couple of weeks and I've been extremely impressed with it.
The screen on it is amazing, the EV-DO performance on it is quite impressive and it's hardly a flimsy phone. Much more solid than the RAZR I've seen in person. Camera pics look pretty good, and you can get a cellphone version of Opera for it, which blows away the built-in OpenWave browser. BT is pretty well done, though I've not tried it with a BT headset. Tethering to my Palm TX is seamless, once they put me under the right PV plan.
Battery life isn't as good as other phones, though with only a 800mA battery, you're not going to get as much as you'd like out of it. Extra batteries are only $40 on the Samsung online store, and with a car charger for the car and 2nd wall charger for work, it's not been as bad as it was in the beginning. Yes, there's no TransFlash slot, though it would've been very hard to fit that in there.
I think the buttons are OK, since they're nice to tap and bring up the display from being dark. One change from the Sanyo's I've had is that they would flip to audible ringer when plugged into a charger, where the A900 needs to be toggled to audible ringer/vibrate.
One more thing. If you have a CompUSA in the area and you're a new subscriber to Sprint, you can get it for $99 with the current week's ad, with the $150 Sprint new subscriber, plus an additional $100 rebate on top of it.