Strangely enough, I've sometimes found it useless on simple things, but quite often it's helped with more abstruse stuff. It seems to have a big vocabulary base.
i find http://www.onelook.com/
a much better one as you can put a ? for letters missing and if it gives many answers you can narrow the search by putting a word from the clue in a box
jan
I use it on and off. Does give some funny answers but managed to get two for me today - material IRONSTONE; and surveillance equipment SNOOPERSCOPE (it also came up with ENTOPTOSCOPE) but only when I put scope at the end - it didn't get them with just the 'miising' letters (I assumed it was a scope).