From vgchartz.com:

The two HD consoles, PlayStation 3 and Xbox 360, have both released a new slimmer model in the last year. The PS3 Slim released in 2009, September 1 in America, September 3 in Japan, and September 11 in Europe. The Xbox 360S was released in 2010, June 14 in America, June 24 in Japan, and July 16 in Europe. It won't be a perfect comparison as they were released at different times of the year, however they both did launch at the same price.

Taking a look at worldwide numbers with each region aligned, it shows the PS3 Slim had a much bigger opening than the X360S, with sales of 585,000 compared to 356,000. However the PS3 Slim with the much bigger opening had a much bigger drop off in its second week as sales become equal between the two, both selling 322,000. The PS3 Slim did pull ahead slightly after the second week and has increased to 75,000 in week seven. The gap looks like it will grow as PS3 sales increased each week and as the X360 will decrease for a couple more weeks, before the release of Halo Reach.
Full Story: vgchartz.com