All the nusual things. No heavy lights, speedos and so on. Simpler wiring. Fewer tabs etc on the frame. No cush drive on rear hub, and I think a straight rear brake rod rather than the articulated thing. Depending on the model, some minor differences in suspension and so on. The F model TT is a nice one - slight engine changes for more power, box-section swingarms, great colour scheme.
I'd take a TT every time personally. But not hard to convert an XT I spose.