ya it depends what games you'll be playing. my phenom x2 does great with everything, except games such as dirt2 and dragon age which utilize more than 2 cores a significant amount. other games using more than 2 cores will start hitting the market soon as well but im personally not sure if i'll be upgrading to a quad myself now.
when i think about it the amd phenom ii x4 has pretty much capped since their 965 is a base clock of 3.4 ghz. there isn't much improvement there until they come out with a new line of processors (unless they really try to make a 975 or something with 3.6 ghz base clock), but they are all the same processors otherwise. same thing with the i7s.
so i think since i already have a phenom ii x2 kicking up dust in any game i throw at it right now, i'll be waiting to upgrade to a quad when new lines come out and either get those, or get the current line at a cheaper price tag.
price to upgrade ratio just doesn't justify right now - and as for buying one right now i think the same applies, go with the faster phenom ii x2 since it is the same price, and OC that sucker to near 3.8ghz on stock air (if your case has good cooling) and dominate games with duals for now until probably 2nd or 3rd quarter this year when another upgrade will be available