Some free hosts are fine for years (but to find them is like finding the "needle in a hay stack").
What really pisses me off: when they start to re-direct traffic, even if it's "only" foreign language traffic... That's the quickest way to get blacklisted with lots of people!
Personally I accept the top- and buttom banners as long as they're clean and small(-ish).
I think it was Pimpserver who had a top banner some two years back which implied child abuse (something like "Daddy's little darling") - that got them onto my blacklist the first time I noticed it.
And no console hell from your 404-pages (or even worse: forced 404s by deleting selected files or suddenly lowering the file size limit) - please!
That's cheating your webmasters and the surfers
I guess there can be money in free hosting if you keep it clean and build yourself a reliable reputation.
A word of caution: since too many free hosts cheated with "bannerless" hosting most TGPs blacklist them now automatically...