I've gone solo maybe five times (20 percent or so), and it was fine.
I noticed I actually tend to do more gaming (two or three slots a day, rather than one or two slots a day) when I'm on my own, though I'm not entirely sure why that is. It might be as simple as not having to, for example, wait for the other guy to finish his breakfast before heading out.
I have a lot of friends whom I only see at GenCon, so there's no lack of social interaction if I'm on my own. If that weren't true, I don't think I'd enjoy going on my own.
That said, I do usually go with the same friend, year after year, and I enjoy the "deconstruction of the con" talks we have. It's fun to talk about why this GM was awesome (or sucked) or the weird/problem/fantastic players we end up with at a table.
It's interesting how often we both get the same overall impression of the con ("best ever!" or "enh" or "is it still worth attending?"), even though we're doing our own stuff through at least 75 percent of it. It varies to some extent, but I don't think we've ever actually had extremely different overall views of it.