Reading your WebLog's Referer log page, to see who's linking to you.
Unfortunately, some systems dump referer data quickly, only showing you the last 24 hours.
Web Service idea:
Register your WebLog referer page, an it emails you ~daily when a new (non-search-engine) Referer shows up. Problem - some blogs/hosts don't provide the data in a way which would be easy to parse (e.g. my IMeme logs (a) are in a month-named file, instead of an unchanging-named "current" file, and (b) the Referer data is just one section of it, so parser would have to figure out where to start and stop parsing).
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