There's a slight advantage to doing it at the registrar because it keeps the hit off your servers. This is assuming of course that http://foo.com/bar will get redirected to http://www.foo.com/bar rather than just having everything redirected to the http://www.foo.com.
That's interesting. Currently I have 2 different domains at 2 different registrars. In each case I have the bare name, www and other subdomains as "A" records, not CNAME.
So it doesn't matter if people use the www prefix or not, since both point to the same IP. And with this configuration I've had no trouble with MX records.
If the goal is www/no-www transparency, there are other ways to do it, but using a simple DNS setup seems like the least hassle.
Great point. And candidly I never actually do this myself (CNAME on the bare domain), I just point it at the server and let apache/nginx handle the redirect.
Edit: I'm wrong. See tadfisher's comment below.