Privacy and Gmail

Google is starting up a free email service called Gmail. A lot of it looks pretty awesome -- a gigabyte of storage, and full and powerful searchability. But I'm not sure what to think about one of the features. Here's what Google has to say about ad placement:

There are no pop-ups or banner ads in Gmail. Gmail does include relevant text ads that are similar to the ads appearing on the right side of Google search results pages. The matching of ads to content is a completely automated process performed by computers using the same technology that powers the Google AdSense program. This technology already places targeted ads on thousands of sites across the web by quickly analyzing the content of pages and determining which ads are most relevant to them. No humans read your email to target the ads, and no email content or other personally identifiable information is ever provided to advertisers.

On the one hand, I think this is a brilliant and innovative idea, and takes ad-targeting to a smart new level. On the other hand, the idea of having the contents of my emails scanned -- even only by an automated process, makes me a little uncomfortable. Possibly, this is just an 'ick' reaction that I should train myself to get over. Or possibly, there's a genuine privacy threat lurking. Thoughts?