Definitely put in an SSD! Benefits? I sold my half share in a rather temperamental MacBook Pro to my son, and spent the money on a refurbished HP Elitebook. Not slim and elegant like the Macbook but performs better! As it came with a 'free' docking station that had a DVD drive, I put in an 250GB SSD to replace the HDD and moved that into the space created by removing the DVD drive.
I now have an even speedier laptop than before, starts up from cold in between 10 and 15 seconds. Things like Photoshop and Lightroom load up in a flash and anything that's drive intensive, like Hauptwerk (a virtual pipe organ that loads all its pipes into RAM before you can play a note) is way, way faster than before.
I was so impressed, I got another drive and put that in as the main drive in this PC, with Win 7 installed (I've already had my say about why I'm not upgrading until software or drivers force me to), leaving the previous HDDs still there, one of them running an entirely separate XP installation with all my music and recording apps on it. When I upgrade again, I'll go SSD all-round.
Any downsides? I've heard reports of them failing. "Avoid Seagate", someone told me - too late, I already had two and, touch wood, have had no issues with either. My son's had a couple of SSDs fail but he 'thrashes' his computers for heavy gaming and photography. The SSDs in our servers (we're really wired up here - son looks after servers for a living!) are all fine too! In any case I back up all my data to an external HDD regularly (as we all do, don't we?) so if the worst were to happen, I'd only lose a day or two's data.
So I'd say "Go for it!"