I just saw a text ad in this article (it might not be here anymore due to rotation):

"Sponsor Spot: Your customers use Google throughout the buying cycle. Advertise on Google and stay with them all the way. Google does 1/3 of all searches, with more than 10 billion B2B searches a year and keyword-targeted ads that reach an in-market audience. Learn more by clicking here or email b2b@google.com."

The choice of place (Line56) and copy shows they want to reach out enterprise customers. Seems organic growth can only take them so far, and they eventually decided to start advertising as well (did you ever see an ad for Google before?)

Update: Robert tells me Google started advertising its search appliance last month, and he saw ads for Adwords on Clickz about two weeks ago.

07/05/02 update: saw a button ad on BtoBonline today.