If the hard drive is truly your bottleneck, a SSD will definitely be of help. I have one of these:
http://eshop.macsales.com/shop/internal_storage/Mercury_Extreme_SSD_Sandforce
The difference in this line of SSD drives is that they don't get slower over time. This helps me maintain my speed even though I use the drive as my primary system drive. SSD leveling also helps with the speed over time issue.
As for the speed difference, I use a Mac with VMWare Fusion running my Windows (I develop primarily in Visual Studio). My Mac boots incredibly fast. In fact, my wife has a similar Mac without a SSD (but she has a 7,200 RPM drive). My Mac can boot into the OS, boot Fusion, boot my Windows and be in Visual Studio before hers comes to the login screen.
In short, I find a SSD to be EXCELLENT for development work.
