I think branded links are perfectly valid because the quantity of people using that brand is a clear signal of popularity.
I don't think it might work, unless and until they have some impeccable brand. In the first penguin update, tons of wordpress theme sites and some other big brand sites took a hit just because of sitewide footer links, some saw recovery right after cleaning most of such links in the next data refresh.
I'd say I hoped that would spell the end of forum spammers
You are right about it, i don't think it would be easy to nail down. They might have put this point up as a scare tactic. As of now, in my niche the 2nd site in serps has handful of links in the forum sigs, but he has played it differently, he has 1 posts each forum, puts in his link in the sig and now after Panda - Emd - Penguin - Page Layout he is ranking 2
OK, who defines which directories are quality, by who's standards, Google?
That should not be too difficult, just search for Blue Widget Web Directory, pick top 5 results and vet them, if they are not offering deep links, no sitewide links, don't allow custom titles and if their backlink profile looks clean then its good to go i believe.