BestBuy said stores will get 100 to 150 units (total so divide by 12 or 18, respectively. Only stores w/ Apple areas will have the 3G version & stock 150 units).
Sams web pages shows 10 or so stores that will have them. No others will.
Walmart may have 20 units total per store, but guess smaller stores will have none.
Target is likely to have limited stock too -- maybe 75 total (again divide by 18).
Each Apple store is likely to have avg of 100 of each model -- more in the bigger stores -- though some colors, sizes may be short shipped. I know the 16GB 3G was shorted at first.
So odds are one is better off being #200 in line at Apple than #30 at Target. Also Apple is a master at launches and checks people out in lightning speed so the line may be long but will move very fast.
Of course if you want a 3G version then ATT or VZW might be good alternatives but they are slow as heck checking people out.