Pandora’s box is open. We may not realize it, but there are a whole load of things in 1.5 that may trip us up. This is more about not moving to 1.5 that moving to it.

Developers who develop on 1.5 will, by mistake, use methods only in 1.5 (Boolean.parseBoolean etc)

Autoboxing and Unautoboxing will compile on 1.5 as 1.4 source, but unless the target 1.4, it wont run in 1.4 as the java.lang.Object is different.

And the real gotya for me is, libraries with generics in wont run under 1.4….. so all those Apache dependencies wont work and we will be stuck, with bugs back at Lucene 1.9.1, pluto 1.0 etc etc etc. Eventually everyone has to move, this is no longer a unidirectional problem, its become bidirectional…. so when do we move to 1.6 :)