Uncle Grumpy
Devout Dirtbag
^ This.Everyone and I mean everyone looked at your rear mech first, it didn't matter what you were riding, rear mech first, instant judgements made, opinions formed within milliseconds before anything else
For some reason people see the rear derailleur as some sort of highly important gadget. After all, it swaps between sprockets and that's what makes the bike rideable over all sorts of topography and terrain. The fact that (at least until electronic drivetrains) it is simply a cage attached to a sprung parallelogram and the shifter does the work is irrelevant.
A friend of mine got all excited about a bike at the LBS that they had trouble selling before the next years models came out, so the shop upgraded the rear mech to XTR and he jumped on it as though it was the bargain of the decade. The rest of the bike was all LX - but it had an XTR rear derailleur.
Personally, I find shifters to be the place where I notice higher spec the most - better feel at the fingers. Chains and cassettes too, better quality and durability is more important than the pose value* of a rear derailleur.
Grumps
* having said that, I'm guilty of hoarding SRAM X0 9sp rear mechs... so pose away.