There is no definite rules as to if you're going to need a camber kit. If you lower your car, odds are your camber will be compromised. The question is if you are willing to accept the added tire wear associated with excess neg. camber.
I have my car lowered with H&R sport springs. That leaves me with about a 1.75"drop in the front and 1.5" drop in the rear. I'm riding on my stock shocks till I get the dough for an upgrade, and have been like this for only a little over a month I guess.
My rear had about 3 degrees negative camber on either side. I did the bolt and washer trick (search that for more details) and that fixed me right up. The front wasn't thrown off that much, and I am going to watch my tire wear and see if I need to get a front camber kit.
Camber is not the only effect of lowering. Your wheels can develop toe (in or out) and this too can cause uneven tire wear. Plus there is caster (again search) but I hardly understand that one myself.
Hope that helps...I was a newbie not long ago myself.