The SSD speeds come at a price.
1. SSD’s are very expensive when comparing to HD’s. At $300 for a 240Gbs SSD vs. $70 for 1Tb 7200RPM HD it’s a no brainer. I Raid 0 my boot drive(s). Since data integrity is not relevant, I don’t care if it craps out. All my stuff is on my internal backup drives.
2. Limited storage space. We’re at a point where you can get 2TBs and 3TBs HD’s. The largest SSD’s I’ve seen so far are 600GBs, unfortunately the cost is $1154 (not a typo). That’s the cost a new decent laptop or SLI\Crossfire setup for your desktop rig.

If this was a laptop I would say try the Seagate Momentus XT 500GB Solid State Hybrid (unless you wipe with 100 dollar bills then go for an SSD). You get decent storage plus fast boot speeds. But from all the articles I have read so far you won’t see much advantage on desktop computers when using one of those.

I setup an OCZ 120GBs SSD on a friend’s laptop and it cut the boot time by half (she has a semi decent HP, so I didn’t expect much from it). On a desktop you will see even more of an improvement as long as you have a decent on-board controller and CPU (super cheap mobos need not apply, that would be like putting makeup on a pig)

If you are willing to spend the money then go for an SSD. Otherwise just dump two 1TBs 7200’s into a RAID 0 and stick with it until the SSD’s come down in price.