1) Language incompatibilities: VFP 6's program(-1) etc., won't run in prior versions.

2) MNX/MNT conversion to VFP6 -- still usable in VFP5 since only increases numeric precision from 1 to 2 in the field called LOCATION

3) In my Config.fpw for each version, I run a program 'DEFAULT.PRG'which allows me to customize each interation -- been using this for years, since one of the functions is a list of directories ( read: projects / customer work ) where to begin. In that program one may test the VERSION() and apply appropriate settings to to _Screen or whatever else you wish.

4) Really happy situation: VFP6 EXE's and APP's can 'DO' VFP5 APP's, but VFP5 APP's will claim that VFP6 APP's are from a prior version ( really a later version, but that's what VFP5 claims )

5) I am loathe to remove any prior Fox version, since I find the HELP topics for legacy procedural coding have been severely truncated in the current versions. So, I even have 2.x for Windows for those instances when I run into such code and can't remember what the parameter list / whatever...

Hope this helps...