Generally, wide rangefinder lenses on mirrorless digital bodies exhibit problems (excessive light falloff, even color shifts) due to sharper angles under which light hits the sensor. These are correctable in software (you have to generate a profile yourself, and then apply it to camera files), and several modern sensor models are advertised as built to accommodate this.
I've never heard of SLR lenses having similar problems. Perhaps the more invasive fisheye lenses that required mirror to be locked up.
As far as usability goes, it's not really that bad. Losing out on meter coupling doesn't matter that much, although you are pretty much stuck with A mode. If you'd rather set the exposure manually, you can just reshoot right then and there if you screw up. Yes, you have to stop down to shooting aperture manually (all adapters I've used keep the lens aperture stopped down to the value selected).
I agree with Yashinoff that the prices of old manual lenses have skyrocketed, but buying old glass is sometimes the only way for a digital user to get his hands on a decent glass without breaking the bank. Yes yes, if he didn't sign up for the 18 month digital programme he'd have the money, but baby steps, people

After all, one of the reasons I've started shooting film was because I fell in love with my 50mm OM prime's aesthetics.
They just don't make them like they used to.