Gotta say I love FileSeek, as it does what it is supposed to do and does it well too. Unlike, say, the integrated Windows Vista search. Despite setting Vista to search non-indexed files and to always search file contents and adding .pas and .dpr using the plain text filter, it just doesn't want to search for the word "memo" in a bunch of Delphi (*.dpr|*.pas) files. Having wasted hours and being annoyed by that piece of cr@p for the last time, I finally came across FileSeek and it did the job in seconds.
One suggestion I have is that it'd be really nice to be able to install FileSeek as a replacement for the default Windows search (that pops up when you hit Win-F and when the search-box in Explorer is used). It's no biggie, as the context-menu option is quite useful as well, but I thought I'd mention it anyway.
For more information on the search protocol (added in Vista SP1), you might be interested in this:
http://support.microsoft.com/default.aspx?scid=kb;en-us;Q941946