The current "slices"/"Dataflow to this" feature is very powerful...it has already changed the way I navigate through code.
It would really rock if Diana final would provide some improvements:
Allow me to select scope. Right now test code is completely polluting my DFA graph with noise
Allow outgoing navigation / "Dataflow from this"
Allow to group the graph by the expression of the edge: I'd like to aggregate all graph endpoints that cause the current variable to be populated with a null value, etc
Perhaps integrate the UI with the "Call Hierarchy" feature.
Interestingly, Eclipse 3.4 provides something similar to "Dataflow to this" already, allows some filtering (usable enough to exclude tests), and integrates the feature nicely into its "Call Hierachy" UI.
Based on experience so far, the value of DFA navigation is very high - please continue expanding and polishing the feature :)