I got an invite to create a SO Careers 2.0 profile a few weeks ago. After getting to over 150 completeness, I received a batch of invites (I think it was 5, but I can't remember).
About a week later, I received an additional 15 invites, along with an explanatory email that stated they were due to my open source involvement. OK, cool.
But, it seems that each week or so I'm getting more invitations, and I have no idea why (no explanatory emails). I remember getting a batch of 14, and then some more, and today I got yet another batch, this time of 12 invites (am I getting one less each week?).
So, why am I getting all these invites? I'm currently at 59 and all I've done is fill out my profile!
UPDATE: Just realized that invitations show up in my inbox notifications, and are hence trackable. Here's the timeline:
Jan 11: 5
Jan 12: 5
Jan 18: 15
Jan 25: 14
Feb 1: 13
Feb 8: 12
Seems like it's every week since the batch of 15.