It's fun reading through this year-old thread. As someone who's on the verge of a big upgrade, it's also fun looking back on my own history.
1990s - EOS Rebel (my dad's camera that I used throughout high school)
1996-2000 - Gave up photography during college
2001 - EOS Elan 7E (Decided to get back into it. I'd always wanted an Elan 2E. This seemed better!)
2004 - Digital Rebel (An inexpensive digital SLR...no more costly fim processing)
2007 - SD800IS P&S (Wanted something more portable)
2008 - Sold Digital Rebel (Wasn't using it much anymore)
2009 - 40D (Caught the photo bug again and chose this over the 50D.)
2012 - S100 P&S (Needed to upgrade my point & shoot)
That's how it stands today (40D + S100). But, I've recently been taking more photos than I ever have in the past, including volleyball and basketball in a dimly lit gym. And the 40D is starting to show its age. I still love a lot of things about the 40D, but the high ISO performance, AF, and lowish megapixel count are starting to matter.
It's between the 6D and the 5D3, but the 6D seems like a bit of a downgrade is some key areas (FPS, cross-type AF, build quality). Unless the 6D sensor is game-changing, I'll be getting a 5D3 before long...especially since the price keeps dropping! I'm hoping the 5D3 will give me at least 4-5 good years.
I change the body once its limitations begin to hinder my shooting ability.