I have used every version of Lightroom from the pre-1.0 up to 5.0. Overall its great, but there is one little thing that has bugged me every time. The process of upgrading an individual catalog is to take the existing name and add a -2 to the end. I think this is the wrong way to do it. If I am upgrading from 4.x to 5.0 then the 5.0 catalog is the one that I want to keep forever and I most likely going to delete the old version of the catalog. Ideally, I think you should make the new catalog match the previous name and give the old catalog a -lr4 (or-lr3, or -lr2, or -lr1) at the end of the name. If you really don't want to change the existing catalog, I would prefer you go to -lr5 instead of -2. With either of these changes, when coming back to the folder at a later date I will have some clue as to what each of the files is.