It seems Google hitting the proverbial 'paydirt' with monetizing its business through AdSense has not gone unnoticed. 

Microsoft has unveiled plans for its AdCenter platform and Yahoo! has launched its Overture follow up, Context Match.

As we near the eve of Web 2.0 (or 1.5 -- however you like to slice it), the focus has been on the big three (Google, Yahoo! and Microsoft), who have been launching new products, revamping old ones, and snapping up new technology in an effort to one up each other.

As the big three move in to carve out their respective share of the established and highly lucrative advertising market, it's interesting to see the periphery players emerge who might well shake up the landscape of Web 2.0.

eBay, which has been residing in its owncomfortable niche, is making quite a play with the pending launch of its AdContext affiliate program, which was unvelied alongside many new strategies and programs at eBay's 2006 Developer's Conference.

The crux of the AdContext platform is the same as the aformentioned AdCenter, Context Match and AdSense programs -- placing context based ads on individual web pages. 

The twist is that contextual auction items will be listed instead of short text ads.  In the short text model (AdCenter, Context Match, AdSense) the affiliated web-site is paid per-click. In eBay's model, the affiliated web site will be paid a portion of the listed item's sale price (there is still no official word on whether this will be the revenue stream model as it seems like it could become awkward).

This is a deft move by eBay and should sound alarm bells for the Big three. Their incumbency in the new paradigm of web dominance may not be set.

In particular Yahoo!, which has just partnered with eBay to provide advertising solutions to the eBay family of sites, should take note.