I've had this conversation with a few people (anesthesiology is one of the fields I'm strongly considering) and my impressions are:
1) A lot of it is hype and people complaining for the sake of complaining. In the environments I've been in, MDs and CRNAs have gotten along just fine.
2) I have found that especially in academic centers the CRNAs are often there to relieve the anesthesiologists so they can have decent hours. Even during residency, the hours aren't nearly as bad for anesthesia as they are for, say, surgery (and remember, you need one anesthesiologist per surgery!). This is in part thanks to CRNAs taking over the basic, not-too-challenging procedures that just take time.
3) At least here, the CRNAs allow the residents to be in the good "teaching cases"- the more complex, elaborate surgeries. Meanwhile, CRNAs can take the bread and butter stuff.
4) There are PLENTY of things CRNAs can't do, and if you're at a decent hospital, they won't be allowed to do them. MD anesthesiologists won't lose their jobs because we're still better qualified to do, say, a complex transplant case or a very difficult trauma case.
5) Let's not forget that you can also subspecialize in stuff like critical care (running the SICU), pain medicine, peds, etc. Correct me if I'm wrong, but CRNAs can't do these things.
So, take this with a grain of salt because I'm getting this as a third party, but in my experience it has seemed to be a positive (or at least not super negative) phenomenon. Of course, I've only been in big academic hospital settings- I'm sure the CRNA thing is a much bigger problem at smaller community hospitals and private practices, where the big complicated MD-only cases aren't really done. But anesthesiology as a field can't and won't die. It may be moved farther and farther away from the smaller practice settings and into the bigger hospitals, but we'll see if that happens.
And as always, OP, consider what you see on SDN carefully. People enjoy the anonymity of the internet not in small part because they get to complain and whine without retribution or (personal) judgment, so there's a great deal of negativity here. When I was applying to med school, there was a lot of negativity about the application process- but it wasn't nearly as painful as people said it would be, just tedious. Then I read tons of posts about how horrible and miserable and soul-draining med school is, and while I certainly have my bad days, I have still found med school to be really, really cool. And of course, let's not forget the "medicine is going to hell" posts written by people "wanting to give advice so we don't make the same mistake" but really just wanting to vent their frustrations. So if you see a forum and the general mood seems to be negative, assume it's because of some herd behavior type of situation and ask REAL anesthesiologists around you who work in a practice setting you're interested in how they are doing with the CRNA thing.