I have been chain running TotC 5/Heroic as much as possible to try and catch up and frankly, wow, the difference in every aspect of play is astonishing. You forget just how much of a difference it all makes, until you suddenly find yourself effectively back in time on a character with the stats you used to have when things were hard. Going from a 35k health pool to a 27k one (up to 30 now, thanks to TotC) was a huge wake up call that made me adjust my pulling strategies, use of my cooldowns, and even how I go about generating threat. As all my stats improve I'm finding myself lowering my foot to the floorboard, so to speak, but in a way I think it's a good thing to be reminded every now and again that you can't just tell people starting out in blues and greens to do what you do in your full raid epics.
It's an experience you can have in other ways, of course: taking your alt rogue to DPS a heroic and being shocked at how much lower his DPS is than your DK main, for instance. So I posit to you, gentle readers, how have you found yourself minding the gap?