The Senate picture is pretty clear now. Democrats have nine solid pickup opportunities, one of which is a lock. In all the other campaigns, Republicans lead by at least 14%, pretty much making them a moot point by now (they have been removed from the chart as a result). So, the strategy for the DSCC is straightforward: dump money into the other eight campaigns. The DSCC probably doesn't even need to spend any money defending Lautenberg or Landrieu, given the polling situations there. Maybe a little bit, but not much.
The best-case scenario for Democrats is now 59 seats, since Lieberman is a goner after the election. The target, as I explained two weeks ago, should be 58, because that get us the employee free choice act (if Obama wins, of course). I think the best hopes for progressives in the next two years is a large Democratic majority, plus Obama, that ends the conservative governing disaster while implementing technocratic stop gap measures and, most importantly, positive progressive feedback loops like the Employee Free Choice Act, D.C. voting, net neutrality / open media, election reform and, if things go really well, immigration reform. Maybe we can't get everything we want in the next few years, but we can work to institute the feedback loops that will continue to make America more progressive. Combined with demographic changes and improved progressive organizing, down the road those feedback loops should make America a much more left-wing country.