It varies from store to store, and day to day.
Some stores get tons of inventory...of ALL types of iPad 2s...and some stores don't get as much....or only specific versions (i.e. Verizon models always seem to be the last to go).
It just all depends on how much effort you want to put into it and if you are flexible.
I only wanted ONE type of iPad 2...ATT 64GB Black...and I lucked out very quickly (5/13 purchase). I went to the Apple Store in Manhattan Village on that Wednesday and Thursday morning...first in line at 0800...and immediately found out that they did not have what I wanted in stock.
I went the following day, Friday, to the store in Santa Monica...first in line again...and got what I wanted. The Santa Monica store had far more stock than the Manhattan Village store.
The effort was worth it, and all told, between the 3 days, only took about 3 hours of my time (with travelling to/from home). Great experience. Plus I had never before experienced the social aspects of waiting in an Apple Store line...thought I normally HATE standing in line, and it sure helped that I was first on each of the days.
At the Manhattan Village store, I found out almost right away when I arrived. I was at the Santa Monica store extra early, but the employees saw me and quickly assured me they had virtually everything in stock and would be handing out tickets at 0800, which they did promptly and cheerfully.