Is it worth upgrading the MacBook hard drive to an SSD

I have a mid 2007 white MacBook. I don't currently have the money to get a new computer (even though I'd love to). I was thinking with all the good reports coming out with the SSD performance in MacBook airs, perhaps I could get a speed boost of my own by replacing the hard drive in my computer with an SSD. I don't need a very big one so I'm thinking of spending no more than $250, but hopefully less.

The first question I have is has anyone performed the upgrade on that model of MacBook and do you have recommendations for SSD drives and tips for doing the actual upgrade?

The second question is do you think that it's worth plunking a hundred fifty bucks into a machine thats getting to its end of life cycle. Perhaps the upgrade will give the computer some new life and I can feel happy with it for another year if I can't get the money together for a new computer right away. On the other hand, is it better to just put that $200 into a piggy bank to start saving for the new airs coming out?

If it will help answer this question this is how I use my computer:

Apps that are always running:

Transmission
Dictionary
Preview
Safari (only a few tabs at a time)
Mail
Skype
iChat
Things
Notational Velocity
iCal
iTunes

Apps that I will run on top of that when I'm doing some specific task (ordered from least intensive to most):
Twitter
MarsEdit
Kindle
Reeder
Pages
Numbers
Keynote
Word
Excel
Powerpoint
iPhoto
GarageBand
iMovie
Miro

I usually run one or both of the office productivity suites at full blast, with multiple documents open in each, when I'm working as a math professor. Sometimes I run Photoshop, XCode, Coda, but not that often.

So, hopefully that helps clarify my MacBook usage.

Also, if you recommend waiting, not upgrading to SSD, but just waiting to get a new computer, do you think I could do this kind of usage on a 13" Macbook Air, or should I really think about getting the 15" Macbook Pro?