Apparently, in exchange for minor leaguer Jeffrey Marquez.
Marquez is a 24 year old RHP who was a first round pick in 2004, and who BA didn't include in their top 10 this year. He had a rough season in 2008 and doesn't strike out a bunch of guys.
Unless there is someone else of significance going to Chicago, this looks like a salary dump, to me.
And just a season after the ChiSox gave up Gio Gonzalez and Ryan Sweeney to get him.
UPDATE -- The full deal:
The Yankees traded infielder Wilson Betemit and minor league pitchers Jeff Marquez and Jhonny Nunez to Chicago in exchange for the switch-hitting Swisher and minor league pitcher Kanekoa Texeira
Picking up Betemit isn't bad. Nunez also didn't make the BA top 10 list for the Yanks.