Web pages with "search" facilities that don't tell you whether the search is by phrase or by individual term... and whose "advanced search" doesn't either. If you're just using google's site search, fine, most of us are familiar enough with that to get how it works - but plenty of sites are using special search facilities.
C'mon guys, this is not something you leave out. It's not information you tuck 5 clicks away buried 8 screenfuls down some random help page. You put it right there, close to the search box. Even better is if you can offer ways to do both (such as "use quotes to search by phrase", which conveys in 6 words that (i) otherwise, you're searching for individual terms, and (ii) searching by phrase can be done in a natural way).