A great number of people including institutional investors and hedge funds are only there for the flip - they give enough commission to their brokers to ensure that they get good allocations at the issue price. And since they are good customers the lead manager will turn a blind eye to them repeatedly flipping at the open and thus depresing the price.
In the case of a good deal, a popular deal for which there is great demand, this does not matter too much for the lead manager. There are instances where institutional investors will want to keep the stock and buy more in the aftermarket. Google perhaps.
In the case of a bad deal, many, many people will flip their stock and thus the syndicate can not hold the bid at the issue price. If you look at the volume on the first day of a typical IPO you will see that it often exceeds the entire amount of stock issued.
In the case of Vonage, they were dumb enough to double the amount raised. They were also dumb enough to price it at the top of the range. In the case of a popular deal this often does not matter. In the case of Vonage there appeared article after article in the press damning the fundamentals of the company.
So, add all this together and you have the usual recipe for a crappy deal. I don't claim I always get it right but I did avoid this one. I may well be wrong on Master Card but I am avoiding that too. The markets have been too shaky for such a huge deal and the comments on the fundamentals have not been too sparkling.
I tend to veer on the side of caution. If you indicate 20,000 shares in 5 places on a huge deal which goes sour, it tends to hurt.