[arfrank]

http://adwords.google.com/support/aw/bin/answer.py?hl=en&...

Excerpt:

When someone searches using Google Instant, ad impressions are counted in these situations:

  * The user begins to type a query on Google and clicks anywhere on the page
  (a search result, an ad, a spell correction, a related search).

  * The user chooses a particular query by clicking the Search button, pressing 
  Enter, or selecting one of the predicted queries.

  * The user stops typing, and the results are displayed for a minimum of three 
  seconds.

[itblarg]

Three seconds? Yikes. Will be interesting to see how this impacts big money PPC spenders...

[guyzero]

By definition it won't affect PPC spenders at all unless someone clicks on the ad. You can only buy CPM ads on the AdSense network.

[itblarg]

It has the potential to drastically alter search, which thus would drastically alter PPC. The likeliest negative outcome is the gradual disappearance of any traffic driven from long-tail search keywords.

[slowpoison]

It won't affect PPC (pay per click) spenders. It will only matter in terms of CPM (cost per impression).