The phone makes a huge difference.
I have (usable) signal with my nexus one, where my (crap) gravity 2 would say no service.
I've generally had a positive experience.
Basements can be bad (depends on distance from tower, and again, phone)
Concrete buildings are killer (again, depends on distance and phone).
I'm impressed with how well the signal travels, despite the (relatively) sparse towers available.
In my house, the nearest tower is 1.6km away. 2nd floor, I get 3-4 bars and 1-2mbps data.
1st floor, 2-3 bars, 1-2mbps
basement, 0-1 (note that an android 0 = still connected and functional), 0.5-1mbps
That's not bad for 1.6km..
<500m from a tower, or really high up (e.g. 10th floor at work, probably 1km to tower) I get a good 3mbps, if not 5.
I haven't had a dropped call since April 2010.
Call quality has been excellent, though it depends on the phone on the other end. (I have some people call me who are using one of the big 3 [I don't know which one, not self censoring
] and every single time it is horrendous and breaking up, regardless of where they are - and it's not my end of the connection, does the same with landline to their cell)