I run the beta Gmail notifier. Checking netstat on my PC noticed an open connection to directory.google.com. Needless to say, that caught my eye. I've tested a few machines; it's only the one with the notifier, not the toolbar, which have the directory.google.com connection.
I've seen these connections from search engine software before. The Alexa toolbar and the A9 toolbar both connect to www.alexa.com. The Alexa and A9 connection is one of the ways that directory uses to watch the pages you visit and assign popularity to them.
Yahoo have strongly hinted (I remember reading) that web popularity will play some part in their algo. (WebRank). It makes sense that Google might consider it too.
It makes less sense to put this measure in Gmail notifier and not the toolbar (or deskbar, even) though.
I suspect it's probably a fluke. DOS's netstat does all the reverse DNSing itself and Google might just be using the same IP address for the directory as this Gmail function. If you start checking the reserve DNS yourself you'll find slightly mismatched CNAME and A records. Once again, I suspect (and I'm far from an expert, a rookie really) that there's Akami weirdness going on here too.
I think it's a fluke; a result of a chain through CNAMES but one worth speculating on and pointing out.