DISQUS

To answer the title question:
There's a reason why I stopped using MySpace, and the when Facebook gets to this point, I'll move on again: load time/page behavior in hand-held devices.

As our world become more and more mobile, accessing social networking sites from our mobile devices is going to be more important. MySpace only has a mobile version on select devices/operators, Facebook has a mobile site that works for pretty much all.

Now take your mobile device/pocket computer/internet tablet and open up the non-mobile MySpace and Facebook.
With devices with 20mb to 128mb of RAM, Facebook works kinda to pretty good, MySpace works excruciatingly slow to browser crashing.
And that's BEFORE I've logged in!

I do have to agree with Intan and the comment above to say that aside from the nuisance of application spam, the cluttered ugly profiles are the one similarity the two have in common. I'm tired of spending an hour on each profile page looking for one's Walk!
That been said, it's A LOT easier for Joe SubAverage to control the look of their Facebook profile than their MySpace profile.

When will Facebook really be a MySpace?
Once you learn how to block applications and make your friends see what a mess their profiles are, NEVER!

Added Tower Bloxx after reading your post and thank you very much, I'm ridiculously addicted to it now... =)

Apparently 55% addicted to Facebook.
I think the application should also count in the amount of time Facebook per day. I'm online everyday, most of the day, through my cell phone, which limits the amount of full interaction on the actual site for me. Let's not get started on my Scrabulous addiction!
I'd say I'm actually somewhere in the region of 93% addicted, especially if you'd count in group administering and activity.
The 5 different attributes which the app uses are a little vague. Entering gender and being a part of a network is something that everyone ought to do anyway. Having a popular wall is mainly an indication of how addicted your friends are. I can understand the profile editing, and the notes (although I fetch my notes from my blog). There really should be more contributing attributes for this app to work.