While this is good news, I think it should be taken with a grain of salt. Some of the cornerstones of the "classic" mode do not exist when it comes to extensions. For instance:
- no workspace switcher extension offers preview of windows 
- it still will not be configurable
The problems of using extensions for customisations are well known. Combinatorial explosion and inability to set absolute settings (e.g. which extension's element takes left most corner?) come to mind first. It seems that Gnome developers still don't want to budge on that (quote: "We still believe that there should be a single, well-defined UX for GNOME 3"), although by officially providing "classic", they already did conceded at least some the points.
It is also a bit disingenuous to say that people want "classic" "because they are used to certain elements and features of the GNOME 2 UX". That is not the main reason. The main reason is the the new interface is more cumbersome to use and has therefore regressed.
Gnome developers should heed what usability experts have been telling us about user interfaces. The most recent example is Jakob Nielsen's report on Windows 8, which is surprisingly applicable to Gnome 3:
Double desktop (overview v. normal mode in Gnome 3), lack of multiple windows (everything heading to full screen in Gnome 3), low information density (again, full screen windows), reduced discoverability etc.
 This piece of text from Nielsen's take on Windows 8 applies rather well to loss of desktop visibility that came with Gnome 3:
"When users can't view several windows simultaneously, they must keep information from one window in short-term memory while they activate another window. This is problematic for two reasons. First, human short-term memory is notoriously weak, and second, the very task of having to manipulate a window—instead of simply glancing at one that's already open—further taxes the user's cognitive resources."