If you are talking about the 'guest' count in Who's online - that is probably just search spiders - perfectly normal on forums, especially when you happen to get crawled by multiple engines at the same time. I thought you meant there were 700 new accounts opened.
If the board is setup to allow spiders to crawl search pages though, that could certainly bog down a lesser system, and perhaps it's setup to disable the more intense features like search after a certain load point. Hopefully if that's the case, after the spiders pass (usually a few hours at most, this forum is very small) the load will drop below the threshold and search will work again. Unless of course it's been manually turned off for some reason.
