At the time I had considered writing a post expressing my own thoughts on the matter, and then promptly forgot about it. The poll is still open (although probably many of you have voted already) and so I thought (with some external nudging :)) that I'd state my position here (one that I summarized in brief for the poll).
If you'd rather not read any more, here's the summary:
I think it's a bad idea.
And here's why
I understand the rationale behind this: it can be a little difficult to work with ACM. ACM does take a contingency fee that increases registration. The cost of proceedings is a significant fraction of the total budget, and the timelines can be a little tricky to work with. These and more are outlined in the poll document, and you can read all the points being made there.
But that's not why I think this is a bad idea (and I do have specific objections to the claims above). I think it's a bad idea because ACM is not just a conference organizing, proceedings publishing enterprise that has bad taste in style files. It's also the home of SIGACT.
For better or worse, SIGACT is the flagship representative body for theoretical computer science in the US. General theory activities like the Theory Matters wiki and the SIGACT committee for the advancement of theoretical computer science were jump-started by SIGACT. Association with SIGACT means that the work you do is 'theoryCS (A)' in some shape of form.
If you're doing geometry in the US, then affiliation with SIGACT is not a bad thing. It means that you're part of the larger theory community. It means that when the theory community makes pitches to the NSF to get more funding for theory research, you're included. It also helps because there aren't other communities (SIGGRAPH?) ready to absorb geometry into their fold.
While de-linking from ACM doesn't mean that we turn in our 'theory badges', it doesn't help the already fraught relationship between computational geometry and the larger theory community. And while the relationship with ACM is not crucial to the survival of the geometry community in the US, being part of a larger theory community that speaks the same language is crucial.
p.s The center of mass in CG is closer to Europe than many might realize. I understand that our European colleagues could care less about US funding and community issues, which is fair for them. But this matter affects US-resident folks more than ACM's surcharges affect the European researchers, and our community isn't so big that we can withstand shocks to one side of it.