SSDs are a major upgrade
I know you have probably read that SSDs are super fast and all, but I put one in my MBP about a month ago, and I need to reiterate just how drastic of an upgrade an SSD is. And when I say drastic, I'm talking about 15 second boot times (including the several menubar icons I have loading on startup, as well as Quicksilver), incredibly fast Spotlight searches (I always have so many files on my machine that Spotlight never performed quite as well for me as for others) and amazing app launch times.
Many of the times you are seeing a beach ball in the OS, it's hanging because of I/O. I/O is the biggest bottleneck your Mac has (unless you've got a dial up connection, in which case that's your biggest bottleneck) and this really lets your Mac perform at its best potential.
You'll get a little more battery life, but it's nothing to write home about. And the decrease in noise and increase in durability are also great.
You will sink a lot of money into getting an SSD drive if you want one that's more than 32 gigs or something (I spent about $700 on Crucial's 256 gig SSD) but it is worth every penny, and if you were debating getting a new Mac, try this instead, because a 1.83 GHz core duo MacBook with SSD is probably going to boot faster than a brand new MacBook Pro with a spindle based hard drive.
