All this talk about the "scheduled maintenance" is getting me anxious too (unsurprisingly), so I called my dad, who's a grant proposal reviewer at NSF. He said the downtime probably isn't related to the fellowship, since it's only a small part of what they do, and relatively minor in the scope of everything going on at the NSF. However, he did also say that right around now is when applicants should be hearing back.
He's not involved in the decisions committee for the GRFP though, so take his viewpoint with a grain of salt. I'm still hoping he's wrong that that we'll all be hearing back in the next few hours.