One caveat, though: Some may say that SSDs do not stop working or slow down over time, as hard drives do. I've been using SSDs in my personal computers for years now. Some do die and, just like a hard drive, they do slow down over time. Don't let anyone tell you different.
If you do decide to go with an SSD, it's best to order it when you first buy your system. That way, it can be configured correctly by the manufacturer, which will optimize performance and ensure your system's warranty isn't voided.
However, even if you decide to throw an SSD into your existing system as an upgrade, you'll still experience a significant boost in performance, particularly on boot-up and application load times.
If you don't have a few hundred dollars to plop down on an SSD, a hybrid drive is an excellent alternative. Of course, you're still dealing with a mechanical drive that can break if a laptop is dropped while the drive is running, but you'll still get performance vastly superior to a hard drive.
In the very near future, however, buying your own SSD may become a moot point as new ultrabooks and other lightweight systems enter the market. At that point, you may want to consider an entire system upgrade.