SSD Can really cut the load times of all your programmes and the operating system, so yes it can be worth it.
BUT… They're expensive! And they're not very big yet. Best bet is to use an SSD for the OS and any applications, and store all data on a "normal" HDD. OK, goes against the ethos of having all your data stored safely, but you'll notice the performance improvement the most this way anyway.
Besides, you're probably backing data up already if it's important. Though any REALLY important data could of course be installed onto the SSD too.
Keen to try it myself in the future (sorry I don't speak from personal experience, just theory) as I've heard it can halve the load time of an OS and any applications.