I've done a a bit of the "using old lenses with adaptors" - and on the whole it's been fine for experimenting, and playing around with...
though there is ONE lens that I'd really love to get "properly" converted from FD to EF fitting... partly, because I'll probably never be able to justify the expenditure of buying the EF version, and partly because, to be honest, the AF of the "proper" EF lens isn't exactly stunning anyway. It's my old FDn 85mm f1.2L - and i'd want it done "properly" - rather than just stuffing a FDn to EF converter (which, by the nature of the conversion, require additional lenses, in effect they're a "short" teleconverter, something like a 1.1 or 1.2x converter IIRC - but, there's always
"The Lens Doctor" who can replace the entire back end of the mount with a re-engineered setup that keeps the correct focal lengths and doesn't lose any stops of light...
Actually, looking at that page, I'm also half tempted to get the lovely FDn 35-105mm F3.5 (macro) converted...