Interference, poor signals, etc.? If you want a program to something like this, go ahead and write one. I can see that being a handy tool for many users myself, if Apple doesn't have a similar log already.

AT&T may have real 3G coverage in LA, but you either can't seem to find it or your iPhone cannot access the speeds. I would think that if 3G is enabled, it would attempt to access the highest data speeds available in the area. Perhaps it is just a fluctuation, no? Also, wherever 3G is, EDGE speeds should be there underlying it.
I'm not sure if this is a good base for a lawsuit. I've heard a few people complain about their new iPhones in many other places, not just LA. And these places supposedly have complete 3G coverage according to AT&T. My guess? Remember those theories about how AT&T's EDGE networks were revamped for the original iPhone? And how many non-Apple EDGE and 3G devices on the network appeared to be suffering from this? Maybe a similar problem is at hand. Just guessing.