The 0.20 series is supported on 1.3, so an important question is: what is the expected timeframe for availability of 1.4 for those users who are currently restricted to 1.3? Vendors should be able to provide their users with some indication of this. We should at least ask the question in any survey of users. An ancillary question is: what is the user's expected timeframe for migration?
I think this is one of the key factors in deciding. It is very tempting to make the decision based on new APIs etc that make our lives easier, but make the lifes of our users much harder.
Anyone who has worked in a large organisation will know: it is very difficult to upgrade the OS on a server (which is a pre-requiste for later JDKs on some platforms). Large companies tend to have request forms/processes just to copy a single file onto large servers/mainframes, let alone upgrading OS/JDKs.