Can't agree with this enough. If your workload is IO bound, SSDs will make a world of difference. Measure before making a decision though. You'd be surprised what's bound by CPU (Loopt's iPhone and Android builds) and what's bound by IO (Loopt's server builds).
On Windows use perfmon or Resource Monitor to look for a disk IO queue frequently over 1. On Linux or OS X use iostat and/or Activity Monitor.
If you don't check before taking the plunge, you could be in for an expensive disappointment. On the same machine, Intel X25MG2s made a 2% difference in Loopt's Android build time, but a 50+% difference in Loopt's server build time. Don't spend the money if you don't need it.
Also, it may be worth it to spend the extra money on a reputable brand drive. Loopt has had 20+ drive-years on 15 drives without incident, but they're all Intel. In fact, we run our primary user database on 4 X25-Es striped in a RAID-0 configuration. I've heard horror stories second hand from friends who tried cheaper GSkill and Patriot drives and lost some or all their data.
Loopt server developers all get 80GB X25-M drives + 160GB RAID 1 platters. Totally worth it. Buy SSDs for your employees!