I'm on the same boat as swallowed here. I own neither a 360 or PS3. However, I hope to get one this summer.
If so, I won't be preordering.
Even though I did preorder San Andreas, and had it the minute it launched, I doubt I will have to here. I will just go to Best Buy the day it launches and pick it up; shouldn't be a hassle.
LCS wasn't, and I also bought that on launch day (then again, the PSP wasn't very popular at the time, and still isn't a very credited system).
I don't expect having trouble to find it whatsoever, in the case I do buy an Xbox 360 this summer.
EDIT: After thinking about it, I will preorder it, IF I do have a 360, and a local store here is still accepting preorders and tell me I will get it on launch day.
It's only $5 [to preorder], I might just preorder it anyway, to be honest