Google also releases new products slowly and then lets them die. Gmail as a commodity product doesn't have the chicken and egg problem that a social network does - and there's no good example of Google solving a chicken and egg problem which depends on brand loyalty rather than technology (qualifications due to the possible argument that advertising revenue based search was a chicken and egg problem albeit one which was solved based on technology rather than consumer loyalty).

I don't think that Facebook/Skype is a response to Google+'s rollout. I think Google+ is a tactical response to a strategy has been developing for a long time (measured in internet years).

On the other hand, Facebook's announcement probably is a tactical response to Google's timing given the massive investment in buzz creation which has manifested itself in the last few days.