Hi folks ! I'm the Eclipse 4 (Juno) dev lead...this is one of the most interesting Juno threads I've found so far (likely thanks to the screening done by your account registration quiz...;-).
I figured I should jump in with a few comments...Juno *is* marginally slower than Indigo for most scenarios but just by a few %. There are configurations that do experience more serious performance issues though (see https://bugs.eclipse.org/bugs/show_bug.cgi?id=385272
for details). We're working away at these issues and SR1 (just out) covers some but not all of them (as well as containing a fix to allow detached windows to be maximized...).
In any case thanks for the input and feel free to open defects about anything you think is really bad.