Ive just bought the OCZ Vertex 60GB (OCUK special) from a 7200 samsung 500GB HDD.
Windows7 load & shutdown times are down to about 20-25 & 5 secs respectively (which is a bit anal!), but the real improvement is in general PC use. It's the timy seek times that make the difference I think. IE for example is instant on initial load - it used to have a noticable delay that I thought was down to my connection. For me its all about those perceptable pauses you get used to as normal in Windows & the fact they dissapear with SSD.
I've installed Windows7Ultimate plus usual apps (plus Visual Studio2008 & SQLServer) to the SSD, along with Steam. Ive got a farily large profile (documents & saved games) of a few gig plus a few games - the big one is Dragon Age & the free space is about 15Gb+ from memory (no pun intended!). I intend to keep it about there.
My video & itunes install is on the old HDD, as are the steam games I'm not currently playing much (moved with the use of symlinks). Once Ive finished with DA:O, I'll move that install over to my old HDD as well, freeing up some space for whatever is my next favourite game (Mass effect2 probably!). This technique allows games to still be played as usual with no re-installs required. It's simpler just to install games to the old HDD, but getting snappioer loads is nice for my favourite games.
Note - DA:O used to take 30secs+ to load some of the bigger maps from scratch (i.e. not cached). On the new drive, it loads the same map in about 5-10secs.
Ive recently upgraded from 8800GT to 5850 (and REALLY happy with it), but I currently consider this upgrate better bang for buck.
In my opinion, 40GB is too small to bother (no headroom for running the odd game off it as well as OS) - 60GB is probably the bare minimum IMO & arounf £150 is the right price point for me.
IF SSDs get cheaper in another year, I will move the drive to my netbook & get a 100GB+ SSD drive for my desktop, so I don't have to do as much active file management. In my opinion, the admin however IS worth the benefit at this price point.
Dan