It truly depends on the price that will be available to you. If you are an average investor, many will recommend that you pass as FB already has an extremely large number of users that is stalling out in the US. They are expanding in other countries however, the concern is that expansion will not surpass what they've already experienced and you will not get a good return if you invest as an average investor because the growth won't be as great as it once was.
When I say average investor this means that you are not "in" on the IPO and NOT getting the best price. If you are "in," that's a much better place to be, but since you are asking this here, I would guess not. My personal recommendation would be a no on this one. The price will be higher for average investors to get in and you will not be on the ground floor position to make the most money, if any is to be made. I hope that I am wrong, but that's the nature of the stock market. There are lots of things that happen that cannot be predicted or guaranteed. Do your homework and come to your own conclusion before investing in any stock.