I've recently had two refurb'ed EVOs, coincidentally also to fix the non-working 4G on a non-rooted phone (hosed MAC address syndrome). They were both mailed to me by Sprint. There was one available at a local repair center, but it was a h/w version 0002 release-day phone, which I didn't want, since I'd previously had a h/w version 0003 phone.
In general the refurbs were good phones without any troubling flaws. The only minor difference I could tell between either of the two refurbs and my original was that the power button on one was more flush with the body of the phone, which I didn't like (less button "travel"). It was subtle, and I probably wouldn't have ever noticed or cared if it was the only EVO I'd ever had. The second refurb phone felt pretty much exactly like my original phone, which was perfect. (I returned the first refurb because of an apparent problem that turned out to be a software/firmware flaw with the compass, which I later determined affects all EVOs)
The screens were perfect on both refurbs, and there were no signs of any scuffs, scratches, flaws, etc., anywhere on the phone. Each refurb came with a new battery cover.
They did have varying levels of previous usage when looking at the ##786# stats. I'm not sure I believe the call stats, since even my original only showed I'd made like 200 calls, which I'm sure is much lower than reality. The refurbs showed similar call numbers. Data usage on one was in the neighborhood of 2 GB and the other was ~500 MB.
I think it's obviously luck of the draw what you get, but chances are a refurb will be ok. I think the days of getting a new-in-box-never-used phone as a replacement are gone, now that EVOs have been out for awhile and Sprint has a supply of refurbs (at least via mail). Of the 5 repair centers in my general area, there was a total of one EVO available as a replacement (the h/w 0002 one). None of the repair centers or retail stores were willing to provide a new phone as a replacement.
Good luck!