I got an implant to replace a decayed upper molar about 10 years ago, and it's still going strong. In fact, I think it's stronger than my real teeth and has never caused me a problem.
Don't believe those ads that say you going to go in with bad or missing teeth, and then walk out with new implants in one day. It is a multi-step procedure that takes some patience and a degree of discomfort during the process, particularly if you are removing an older, infected tooth first and/or need bone grafting. Be careful to choose a good doctor--you get what you pay for and going for the cheapest and/or fastest could result in problems down the road.