I have used a method to split Steam folder -- when I had a few games on SSD and all the rest on regular hard drive. Found it online -- or someone here suggested it.
Anyhow, the method creates a link from the "homebase" steam games folder to any other folder on the system. So, in principle, you could have your steam games spread across all your hard drives (however many). So, from my experience, it is feasible.
Currently, I'm using SSD for the Windows 7. However, as I found no good reason to have any of my games on the SSD, I moved all the steam games to a single steam folder on a hard drive.
Here's the link: Split Steam Install
Crossfire 2x Sapphire HD7970 OC - Eyefinity 5760x1200 24", 1xDell-U2410 H-IPS + 2xHP-ZR24w S-IPS, Ceton InfiniTV 4, Piledriver FX8350@4.6GHz w/Swiftech Water Cooling, 16GB GSKILL PC3 @1866, ASUS Sabertooth 990FX, OCZ Vertex 4 256GB SSD, 4x Seagate + Hitachi + 2x Sg Ext = 14TB, Lite-On DVD, OCZ ZX 850W PSU, CoolerMaster HAF922, TM Warthog HOTAS, TM T-Flight Stick X, TM Cougar+FSSB & CH Pedals, Saitek X52 Pro & Pro Combat Pedals, TrackIR5 w/TC Pro, Windows 8 Professional 64b