I own a D12-C (black carpet), which is an awesome cab indeed. It was the first Bag End cab I bought, some five years ago, replacing a Peavey 1x15 (Scorpion-Plus). The D12 sounded so much better, both deeper and more articulate than the Peavey. I am driving the D12 from one side of a Chevin A1000 power amp (600W @4 ohm), and the cab does not seem to have a problem handling that much power. I like to think that it will take whatever you throw at it.
The D12's biggest flaw, IMO, is it's physically awkward to handle. It is fairly heavy, and the handles are not in a convenient position for lifting. I put wheels underneath it, but it falls over easily because it's relatively tall and narrow.
I later added a D10X-D which is my preferred cab for most situations. It is the old, shallow type. Very compact, easy to move around, small footprint, yet very good tone. I have also used the D10BX-D (deep version). Surprisingly, the deep cab didn't sound that much better or deeper than the shallow cab, but it's a lot more difficult to move.
Both D10's combined make for a nice stack (and allow me to use both sides of the A1000), with a somewhat more bass-heavy sound than the D12 alone. On the other hand, it seems to me that the D12 will fill any room more easily than the D10's do. One other thing the D12 is also very good at is outdoor gigs, it doesn't seem to care wheter it's being played inside or outside, it simply keeps sounding loud and good. Maybe it's because the rear vents are much smaller than the ones in Bag End's 10" and 15" cabs, I don't know...
