Maybe a little late but here is my 2 cents/experience:

I have a 2.6 app which I just did a straight conversion on. Some of it would run and some of it would not.

If you remember, window (screen) management in 2.6 was a bear due to read level contraints. Someone mentioned modal screens - well, unless you wanted to make a career out of read level management, the best thing to do was to make the whole thing modal. Users do not like modal nowdays because Windows works very modeless and they get used to this and want it.

One of problem with my 2.6 app was in this area. My partner and I attempted to make large portions of the 2.6 app APPEAR modeless thru elaborate window and read level management. Herein lies the problem - if you have an application that has management code like this, in 2.6 this code is scattered EVERYWHERE. Simply removing it is not possible as the logic often involved deciding whether or not to shut other things down before starting something new. In our case it turned into a table management and update nightmare.

The other problem was that we ALWAYS had the following in our 2.6 forms:

1) SCATTER and GATHER to allow user to cancel changes.

2) The ability to start and stop the form (screen) and remember what it was doing on restart (DO .SPR).

To make a long story short, if you have a 2.6 app which was put together in the
normal old FoxPro recommended simple way, the conversion works pretty good. If you have an app in which the developer incorporated the functionality that most good applications have today thru custom and trick code, you will have an ABSOLUTE NIGHTMARE!

I am there right now because the app I am talking about really needs to be able to communicate with 32 bit Access databases among other things.

If you have the second type app, don't waste much time trying to make the old stuff work - just start rewriting now. I spent almost a week just trying to make our old customer info form work right. I chucked it and made a brand new one in
VFP 6 in about a day. It even has more functionality than the old one did.