Yotify just launched its Web content monitoring service. You tell it what you're looking for, and it will monitor specific sites looking for your query to return results. Then it will send you an e-mail telling you.
It's a useful service if you're looking for a particular item, for example, on Craigslist (but nowhere else), or a review of a new Web app on Webware (but nowhere else). The problem is that you cannot easily create a search agent (Yotify calls them "Scouts") that scans multiple sites at once, like Google Alerts does. However, Google doesn't allow for data-aware searches: you can't easily encode a search for 1- or 2-bedroom apartments in Russian Hill (with parking) at $3,500 a month or less. And Google also doesn't give you a preview of your results. Yotify allows you to refine your Scout until you have it right, and only then starts to run it around the clock on your behalf.
There is one Scout that seems to be more Google-like: the vanity search. If you ask Yotify to set up a Scout for your name, it appears to scan against the entire Web.
The upshot: I'd give this utility a grade of B- or B. It would be far more useful if its Scouts were multiple-site.