Can't answer your specific question regarding Premier06 > Deluxe07.
Can comment on Deluxe > Basic - works fine and nothing blows up. Ran
both Deluxe06 and Basic06 and swapped the data file-set back and forth
from one machine to the other.
Recall a similar query in the Intuit Quicken forum in which author was
'downgrading' from H&B to lower version. An Intuit moderator chimed in
with a comment as to what happens to account types unique to H&B - the
account type for these was changed as I recall. Tried a quick search of
that forum but couldn't find the thread - you might have better luck
with a little more perserverance. Bottom line though, as I recall, was
that nothing 'blows up' - there were certainly no dire warnings or
sirens going off.