As the Great Recession bites harder, so the competition for online eyeballs heats up. Within the last couple of days this has been illustrated by two data points: Microsoft’s Bing is off to a pretty good start overtaking Yahoo at one point, and Facebook’s unique visitor numbers are creeping up towards those of Google if one includes Facebook Connect sites.

First Bing. comScore reports that in its first week Bing increased Microsoft’s share of search results pages (SERPs) in the USA by 21%. Now this is from a fairly low base so the increase is from 9.1% to 11.1%, and it’s backed by the massive advertising campaign for the Bing launch so one shouldn’t get carried away. But it is still the first time that Microsoft has taken a bite out of Google so deserves to be noted.

Now Facebook. Compete has just released figures for May showing that US Facebook traffic jumped to 82.9 million unique visitors for the month, plus another 65 million to Facebook Connect sites. There’s a lot of overlap in those visitors so the total for Facebook sites comes out at 113 million. This compares to Compete’s calculation of 135 million uniques for Yahoo and 145 million for Google, with Facebook’s growth curve significantly steeper. As TechCrunch points out, if trends continue, Facebook will overtake Google in uniques by year-end.

For publishers and affiliates, these disruptions in the market mean there are opportunities for PPC arbitrage. Look for ever more Facebook ads – especially those linking to high-payout continuity programs – and, as that advertising marketplace gets more competitive and the easy profits get driven out, watch also for smart buyers to be scouring Bing for opportunity. It knocks loudly for those who care to listen.