It skips over terms that I know are present, and it seems to do this quite often. At first I thought this was because the term had been added after an edit but I know that's not the case now.
Also, I didn't log on this morning but tried running a search and was asked to enter the numbers I saw in a box. It's a new implementation since the forum upgrades but just thought I'd mention it since I'm not sure whether it's intended.
Cool. I've done a test over the past few months with my username (well, the jew part) and reckon it's probably about 70% accurate - meaning it omits about 30% of results. It's consistent about its omissions and will continue omitting them in each subsequent search.