The current information is that the vaccine is effective for at LEAST 5 years, and that there are no adverse long term effects so far.
Of course, for a doomsayer who lives and breathes on fear, uncertainty and doubt, no length of time will be enough. If there were data available for 20 years, you'd just ask, "What about in 25 or 30 years? WHAT THEN!!??"
The vaccine works.
Cancer is a horrible, horrible thing.
The chances of being harmed by the vaccine are miniscule when compared to the benefit.
Information from FDA and CDC on Gardasil and its Safety (Archived)
A few important facts:
1) Until regular PAP tests were instituted in the US, cervical cancer was the #1 cancer killer for women.
2) About 4,000 women still die from cervical cancer every year in the US.
3) Since Gardasil was approved in June 2006, there have been about 20 deaths related to the vaccine.
Well, being dead seems like a long-term effect to me.