SSD's are into no-brainer money now. I picked up a 120GB Vertex 2E (Older model, but still very quick) for £43 Delivered the other day from Overclockers.co.uk, it's just for my new Virtualisation server (18GB RAM, i7
920@3.5GHz). I may even grab another one if I see them a that price again and run RAID1.
We've started replacing any failed HDD's at work with 60GB Intel SSD's now. They are the same price as a mechanical, comfortably hold our deployed OS image and make a huge difference to the user experience. We'll probably actively replace next summer and get an extra few years out of our aging Core2Duo workstations. One of these with an SSD is nicer to use 95% of the time than a brand new £500 i5 machine with a mechanical drive.
I've just worked out I have 680GB worth of SSD spread around my various comps now, and almost 1TB if I include my parents laptops that I upgraded.