Originally Posted by Kroy

I second Sandman - it really depends on the SSD you're getting. Many of them are just not worth it, particularly the lower priced ones. Performance even varies between editions, for example the Intel X25- M is good, the X25-E has faster write speeds but is more expensive. To make matters more confusing, there are first and second (and third etc.) generations. The newer ones of course are better but you need to look closely when you shop around.
As a boot drive only, the M series should be fine. Keep in mind that SSD storage space is extremely limited even today.
If the only reason you're wanting SSDs is that your WD Caviar is failing (blue? black? green?) then that might not be a good reason to spend six times the amount for less storage with a SSD but instead try another drive. I've had great luck with all my WD Caviar Black drives, particularly the 640Gb series.
Hope this helps.