I chose to post my miles to my AC account mainly because I already had what I considered to be a significant number of points there, and didn't want to spread things around to too many places.
And by the time I realized that my travelling was going to be so significant this year, I'd already began accumulated segments and Qmiles with aeroplan, so I didn't want to stop there.
After 2006 my travel should decline significantly again so right now the points in one place is a higher priority than having status spread around.
And right now I'm getting some perks with UA and US, a couple of nicely timed operational upgrades based on my *gold status, as well as E+ seating on UA.