Last time I checked you could only do one NW WP miles award from E-rewards per calendar year. I've already done my $100 / 2000 miles redemption for NW for 2007 so upcoming redemptions go into other buckets.

I don't see much wrong with E-rewards and find the earning rate much better than e-miles (5 miles per survey? 2 miles? I don't even open the emails anymore). The one E-rewards annoyance is that some of their surveys are extremely targeted, so you can spend time filling out a long list of filter questions, then get tossed aside.