Dan,

Personally, I think the most elegant solution in terms of Java EE is
simply to standardize "promotable" transactions. Specifically, JTA could
be modified to use local transactions by default and only promote
transactions to distributed mode as the need arises. The Microsoft guys
have had promotable transactions for ages, I am not sure why we don't
have it in Java EE too. This would make the "lightweight" vs
"heavyweight" debate moot and keep things simple/consistent from a
developer's perspective while most of the systems-level issues are dealt
by the container where these things belong instead of a steady leak as a
development concern.