I have an SSD in my Fedora workstation for my rq tool, specifically for the MySQL database. The speed increase there, because it was dealing with huge amounts of data, was very welcome -- not so much for importing (speed there didn't much increase since all the files being operated on were on the HDD), but for querying it is wicked fast. Besides that, and the built-in SSD of my MacBook Air, I've not used SSD before as it is just too expensive. I'm a data storage junkie, so I opted more for large storage than fast access (and the price per GB of SSDs is a little too rich for me).
Yesterday I picked up the first SSD that I've bought (the other SSD in my Fedora box is a loaner from a friend). It's a 240GB OCZ Agility 3, and it's still over $1/GB which is a bit nuts, but since I have an extra SATA connection in my Mac Pro, I figured I'd give it a go. This rig is pretty good: 2 quad core Xeon CPUs, 32GB of RAM, and 8TB HDD space including the one external USB drive. The only real bottle-neck on this thing is disk I/O, so I figured I would give the whole SSD thing a go, since I knew I'd get better performance.
Using an impromptu timer on my phone, from chime to login screen, it took 3:07.7 minutes, and from when I hit enter at the login screen until all the apps were open and ready for use it took another 3:54.9 minutes (some of this is network-bound, as I waited for Chrome to reload its two windows with 27 tabs, and there are other hefty apps like iTunes (with a massive library), EagleFiler, Daylite, Mail, and quite a few others). So from turning the machine on to when I could use it was roughly 7 minutes. After installing the SSD and cloning my boot drive to it (and doing a lot of file moving so it would all fit!), then rebooting it once so any caches would be updated, I rebooted again and timed it.
From chime to login screen took 35.3 seconds. From login to all items ready for us took 43.0 seconds. So my boot time went from 7 minutes, to under 1.5 minutes all told. I think this is the best $300 I ever dropped. =)