I have been running the 2.6 series on my 600E since the pre-releases and I have no problems at all.
One thing you may want to look into is upgrading your Thinkpad's BIOS since older revisions had a bug that made it virtually impossible to boot Linux at all. I am running the latest available BIOS from the IBM website and it works very well.
I do use ide-scsi though. It helps a lot when you're ripping audio CD's, so ide-scsi isn't completely useless.