Length doesn't matter much to me, but I do find myself not reading things, even if they sound interesting, only because I don't want to start reading something until I know that I'll have the time to continue (um...is that the same thing?). So at busy times, yeah, I totally don't commit to long fics. But I do save them somewhere if I think I'll want to read them when I have more time.
It's not that I see it and say "too long, I'll just skip this one" it's more that I don't like starting things I may not be able to finish.
So honestly, what's really off-putting to me are WIP.