Pretty much no issue unless you have some very funky code. 11 to 12 has been no issue for me at all. Same 7 to 12.
“That’s what’s cool about working with computers. They don’t argue, they remember everything, and they don’t drink all your beer.” ~Paul Leary
Some horror stories regarding items with leading spaces or periods or vv. But one should have "read the rules" way back then. Currently dealing with an FMP5 solution that was forced into 12. Who knew that "[" and "]" would be repurposed from zilch to important? Conversion grandfathers these "errors" but any attempt to reuse or alter will invoke the new FMP engine - no tolerance.
"Washington, DC is to lying what Wisconsin is to cheese." - Dennis Miller