Just curious and for what reasons?
I'm thinking of switching to Canon FD system (from the OM system). Maybe it's a bad idea--not sure but my primary reason is because it's cheaper overall. Which glass is better? Who knows? My feeling is that they'll render images the similarly unless you're shooting to test.
I bought into the OM system because they are pretty and rangefinderesque. OM is probably the most rangefinderesque SLR but it's not a rangefinder, and I lust for my lenses! I'd stay in the system if the glass were cheap, but they aren't. Originally I thought I'd be happy with a 35mm f2 but then I got a 28mm f2 and now I want a 50mm f1.4 and an 85mm f2. I have no plans for digital so if I were to switch to FD now, then I can probably sell these lenses and my two OM2 bodies and have a complete suite of fast lenses (28/35/50/85) with two Canon F1 bodies.