I do not know if others have upgraded, but after spending parts of the last day playing with it, LR 6 is looking good. I am liking the results from the in LR pano-merge and HDR ...but the real difference I am noticing is the processing speed has increased. LR now uses not only the CPU but also the GPU's processing abilities.

Need to play around a little more with the other new features

One quick note, it has created separate catalogs for a couple of projects I had ongoing in LR5. I haven't yet had an issue, but as an FYI.