For great background information about the lawsuit point your browser here.
Groklaw has her inimitable point of view as a US paralegal here.
There is a hint in Groklaw's post that NetApp's close tie-up with Microsoft may have something to do with NetApp going after Sun. She reminds us that Microsoft, at a remove, funded SCO in its litigation efforts against IBM and Novell.
But Sun and Microsoft are also now much closer than they were so we are left in a confusing dead end.
NetApp founder Dave Hitz has set out NetApp's response to Sun's decision in his blog. In summary, NetApp is not backing down. The comments to his post generally disparage NetApp's position and criticise the US patent system.