Recent changes at both Propeller and Mixx have pushed the inevitable forward. Mixx, the brainchild of Chris McGill, has been poised for success for about a year now. Propeller, the once-proud Netscape, was doomed the moment that AOL stepped into the picture.
If recent trends on Alexa (which we all know are not always accurate) give any indication about what is happening, then Mixx is making the move to become the 3rd choice amonst social media sites. Propeller, on the other hand, is heading down, down, down as users have expressed concerns about a lack of communication from the administrators as well as a disastrous redesign that threatened to push its dwindling core of users off to another site (perhaps even Mixx).