Do not dose GHB in terms of "caps". GHB can be made in almost any concentration so make sure you know how many grams you are taking. Like AS, you should do plenty of research before you decide to use it. You really have to trust your source on dosages. When you buy a new batch, make sure to always start low and see how it effects you before you add more. Wait an hour before increasing your dosage.
Do not equate the dosage of GHB to the dosage of alcohol. For example, do not think that 1 gram = 1 beer, 2 grams = 2 beers, etc. This will get you into trouble. It is more like 2 gram = 8 beers, 4 grams = 16 beers (i.e. realize that you are doubling the dosage, not just having another beer!).
I would say that a typical starting dose would be 1 or 2 grams. Increase about 1 gram per hour until you acheive the desired effect. Do not mix your GHB with alcohol or any other depressant drugs as it can have a synergistic effect that could land you in the hospital or worse.
In terms of effect, although it has often been equated to alcohol, I find that it is a slightly different high. Personally, I don't get as silly (disinhibited) as I do with alcohol and I usually become more tired. Actually, I prefer the effect of alcohol as a party drug and would choose it over GHB if it weren't for the damn calories and hangover.