I'm really pleased to see Yahoo taking a more open approach to their paid search relaunch, even posting stub perl code for the Yahoo PPC interface openly on CPAN.
While those code stubs don't help my firm much directly -- we need enough custom code to tie each API call back into our data warehouse and our quota tracking systems and our bid management optimization platform that the Jeff Lavallee's interface code isn't right for us as is -- I am pleased that Yahoo wants more folks to use their API.
Yes, the old closed model offered short term exclusivity benefits to us and our clients. But the old system was creaky and clunky, with insufficient engineering resouces at Overture/Yahoo devoted to it to keep it running (at least that's how it looked from the outside, given availability hiccups). The open API means more API users, and more users will mean Yahoo will build a more powerful, robust, and reliable system. That's a major benefit.
I'm also a believer in free and efficient markets. Even with more advertisers, I think in the long term the 'best' retailers do win -- where 'best' means the strongest brands, the smartest advertising, the most savvy bid management algorithm, the best merchandise, the most solid value proposition, etc. So even with increased competition, I think the new reliable improved Yahoo platform is a win for entire online community, and over time the market will shake itself out, with click fees reaching a dynamic equilibrium and the market making sense out of all the players in each vertical.