I'm against 50% EQM and made a swtich but its mostly personal reasons. I agree with the previous posters though - CO put in enough mitigation to keep a mass exodus of Elites from occurring including:

1. The CO.com or Bus Mgr exection.
2. The actual levels of Fare class that get EQM - If you are booking CO flts or even a CO designated flt (so long as its CO on your ticket) then the reality is that only the most deeply discounted fares get hit with 50%.
3. Competitiveness of other carriers - With apologies to the other flyers out there - most of the other programs just aren't as good as CO's - particularly with upgrade privileges for all but the top tiers.
4. Skytem limits - Skyteam members won't status match CO and Skyteam members hit CO flts with 50% EQM too so you can't switch to NW or DL and fly CO to get around the limit.

That being said the 50% EQM does really push travelers that have:
1. Companies that insist on working with travel agencies. Larger companies (I work for a DOW 30) typically insist on booking through a designated agency. They dimiss the idea of better fares on the internet due to questionable faith in their contracts. What's important to them is a travel agency that consolidates travel do get volume discount rebates and similar arrangements.
2. Needs to fly CO partners - the CO 50% EQM hits at much higher fare classes when flying a partner.

This year I've made a switch to NW but I'm not sure how much my case applies to the general population of Elite flyer. What pushed me were:
1. My company uses the designated travel agency.
2. My company has a relentless policy of always booking the lowest possible fare which is enforced by the agency.
3. I have to fly partners a lot of the time - either because of going where CO won't or because a partner has a lower fare.
4. NW 2X EQM promo - NW ran a promo where you could earn 2X EQM for a few months this year - making a switch a lot easier.

So now I'm a NW Gold instead of a CO Silver and that's with only a few months of flying as a NW member. If I had stayed with CO I'd still be a Silver.

Bottom line: CO's policy has probably hurt some flyers but I don't think its enough the CO is very concerned. However, I wonder if its going to be sustainable in the long term. Cost cutting is today's coporate mantra - more and more travelers are going to be in the same place I was. Additionally, if CO does much more to degrade their program it could start to add up.