I, too, seem to start my new projects in 6 and then migrate (hehe) into 5 at some time or another. My huge issue with 6 is that the animation export does not work at all. There is a weird z-fighting issue that promotes horrible flashing and flickering if you have two surfaces that are close to each other (a blue skin for a lake picture, a driveway on a topography that I need independent, etc.) CraigD has been working with me on and off for months on this issue and I guess they are having a heck of a time resolving the issue.
Another export issue is that 5's default aspect ratio is 4:3 and 6's is 16:9. So if you set up all your scenes in 6 and then save as 5 to get a good animation, every view is different from what you originally set up. This has cost me days in tweaking setups.
6 orbits significantly better on the Intel Mac than 5, so I will use 6 on the bigger models to model some things.
I am probably one of the minority, but I have found the whole Styles thing to be overblown, less than intuitive, and really 90% wasted on me. It would be great if they had a slimmed down 6 that we could use that didn't have all these "cute" features that I can do in photoshop better and with more adjustability. A great feature would be a global texture opacity slider, so you can moderate the overall look of a model, too.
Overall, I have found the 6 release to be fairly disappointing. I am not convinced about the direction SU is heading and I shudder to think that 5 may be my default version from here on out. I hope I am wrong........
And what about Layout? Also quite disappointing, IMHO.