Poser 6 uses external binary morph files (.pmd extension). This reduces filesize, speeds load-times, permits multiple characters to use the same morph deltas (thus saving memory), etc. It's a good idea, but it's still a bit buggy. You can disable the feature via General Preferences, keeping the morph deltas "internalized" as with P5 and earlier. As far as upgrading is concerned, P6 does have some nice features, many of which I consider worthwhile. And you'll be able to play around with the new P6 figures (Jessi, James, Kate, and Ben).