Yes, all the machines I care about are SSD based *only*, no mechanical monstrosities are allowed!
Like all self respected developers, I have more than one dev machine at work, the first one has two 120GB SSDs, the first one is for the OS, and whatever apps I use, the second one is for the enlistment (if you know what razzle is... tfs sources, builds, binaries, everything, esentially the whole workspace); the second dev machine has three SSDs, one 180GB reserved for the OS and apps, and two 180GB in RAID-0 for the enlistment (sources, builds everything). The are no HDDs on these machines.
The OS partition does not store anything but the OS and whatever apps I install. My dev boxes are also are very stable, I don't usually install any dogfooding software there. And the number of apps I install is usually within the single digits. Also under no circumstances I allow any sort of Hyper-V servers to kill off my dev machines performance (not while I'm alive). I have separate machines for Hyper-V.
Then I have my terminal services machine, which I use to connect to other machines (I do not use KVMs or other silly things like that), has only one 120GB SSD reserved for the OS, apps and documents.
Currently, my SSD array is running out of space, so I'm considering adding another SSD to the array, that should increase the performance further.