Cash and cash equivalents is about the only thing you can use with Sun. Expect a lot of fluff assets and capitalized expenses on their balance sheet (witness the sudden evaporation of a billion dollar asset just yesterday - it was a legit accounting entry, but a tax "asset" like that is only good if you're going to ever make enough profit to use it - which doesn't look good in their case).
So book value is unlikely to be a good number (actually it's rarely a good number if you really dig into most company's balance sheets). The only practical measure would be to try to figure their breakup value. Don't know about Carl Icahn, but a takeover and management housecleaning (from the top down) could only be a good thing at this point.