Even better multi-threading support
With the advent of dual core and soon to be 8 or more core processors one way of improving performance of applications is more use of multi-threading.
The new Concurrent package is a good start, enabling low level concurrent features to be used easily. However most of the JRE is still single threaded.
Please provide even better concurrancy, both under the hood (so programs work faster on multi-processor systems even without explicit use of multi-threading) and as more high level components.