This from a media specialist at Google: on how to target gmail with your adwords account. Talk about “entering the conversation already going on in your prospects mind”!
Imagine, someone gets an email about losing weight and your weight loss ad shows up on the right side. Or someone asks about the best vacation rental in La Jolla, CA and bang, your ad shows up right along side the email.
The volume is low on these compared to other forms of site exposure BUT the relevance is high and the conversions have been huge in some testing. May take some creative choice of keywords but potential is great.
Check it out and let me know if you plan to include as part of your adwords strategy. (We can help.)