Mostly business related software like Decision Support software, Datamining stuff, zOS and iSeries emulators among others.
There's no easy way to make these running under Wine, in fact I'm pretty sure there's no way. :(
Atm I still need to run XP and Vmware on it, I have Ubuntu, Kubuntu and am considering to install Snow Leopard (yes, on VMware over XP :D) which might give me a few extra headaches. :p