Honestly? Me. Admittedly, my focus is very narrow -- brand names and domains. But I see an appalling number of good startups begin by blundering in that narrow little area I know. Just as many get it right; yet even the fortunately named sometimes just luck out, without really thinking things through fully. Like playing darts blindfolded.
In the early stages of naming a project and securing a domain, it's so easy. Later it can be horribly complicated or expensive. So I'd love to be there when people have their first discussions just to say, "What about ..." or "Please don't ..." or even "Yeah, that's a great choice ..." Much better than talking to the same people a year or two down the road once they've realized there's a problem.