good questions and I don' t know answers for them - sorry
however, I already asked for the same the last week - no answers
Now about what I think and would like to get comments for it from JBoss-IDE developers:
- JSP support was removed from JBoss-IDE; JSP support (editor, vaidation, etc.) is part of WTP;
So, yes JSP compilation issue was resolved by removing JSP support.
No, you can't use "old" project where JBoss-IDE supports JSP with Eclipse 3.1 and M3 - as result.
Yes, you can compile JSP by validating it in WTP, but some how that has to be Dynamic Web project, where you can setup JSP server (it doesn't have Jboss 4.x as target yet).
I don't know much about WTP yet, so can't help you much there.
To be able continue development I keep using Eclipse 3.1M5 (pre WTP API changes) with JBoss-IDE 1.5.0M1
Hope to find better way around it.