Hmm, a difficult question - but I have a suspicion that in your case it might not help.
First of all, I'm a Windows user and view Macs as evil, but still - I shall try to be objective.
On my laptop I switched my HDD for an Intel SSD (fast on small random reads and writes - these are more important than sequential reads and writes which mainly make for nice specifications and little else) and Photoshop (which sometimes uses large temp files) became a fair bit faster at some tasks.
Adobe Bridge possibly also did when it comes to opening Photographs in CameraRAW - and for all intents and purposes Bridge and Lightroom are similar, but Lightroom adds the catalog and "in house" conversion to JPEG which Bridge delegates to Photoshop.
Overall, the performance with CS4 (CameraRAW 5) is fine on a 32Bit OS, 2,5GHz Core2Duo with 3GB of usable RAM, editing 21MP RAW files from a Canon 5D MK II.
Now I tried Photoshop CS5 - after a new OS install because I broke my OS (yes, my fault - nothing wrong with Windows otherwise), so if anything it should have run well. Well, it ran worse than CS4 ever did. Slower and laggier.
What I suspect has happened is, that Adobe piles on functions, which while they make the software more powerful, also make it a lot more laggy. It really should not have run worse, considering that I would happily edit files in batches on CameraRAW 5 and got immediate feedback, but it did...
Where does the SSD come into this? The answer is, it doesn't. The file that you are currently editing should reside in the RAM - or rather a copy of it. The most you will be writing while changing setting is metadata or an external .xmp file. There is no need for access to the harddrive.
So there is no apparent reason for the worse performance, other than more overhead in the Adobe Software.
Ironically enough though, by 2010, the changes from 2008 had not been too significant in the area of computing, at least on most mainstream machines, and my laptop was fairly powerful for 2008.
What I deduct from that is, that most likely Adobe as just piled in too many functions with too few optimizations into the newer version.
This would happen on any OS - Windows, the apple OS etc.
As a result I highly suspect that if you have issues changing settings on individual images, the overhead in Lightroom 3 is just too much for your computer and an older version of Lightroom would possibly work better.