When I had the mobo outside the case with my XP-120 and Panaflo M1BX 120mm fan, idle CPU/motherboard temps were 42*C / 28*C and full load (dual Prime95) was 61/29 respectively (all at 71*F ambient). I installed everything inside the case, idle went up 1*C to 43/29 and under load 3*C more to 65/32. This is with a Pentium D 830 overclocked to 250FSB, which runs really hot anyway.
So the case didn't hurt things too much - it's not the coolest case out there for temperatures, but does reasonably well IMHO. I added the
EX-34B cage below the top bay (where my DVD drive sits) mainly for the 120mm intake, and I think this really helps. The fans that come with the case are ADDA's rated at 72CFM and 34db, so pretty efficient and not terribly loud (that is very subjective anyway).
The vent holes all over help to provide airflow, at the expense of some noise escaping out. So, it's not the coolest or quietest case out there, but a good performer all around. And, I absolutely love its looks! It was also a pleasure to work in and with, beautifully constructed; everything is smooth and attaches/screws in marvelously.
I'll contrast this case with a Cooler Master Stacker RC-810, which is what I first bought for my new rig. I ended up putting my other/older system into the RC-810 and using the Lian Li PC-V1200B for the new system, so that'll tell you how much better I like the Lian Li.
The RC-810 just doesn't have the solid feel and fit and finish of the PC-V1200B. I had a problem installing my PCI cards because the "slots" in the case where the bottom of the card goes just didn't line up that well - it was a real pain and left me with a bad taste. The 4-in-3 modules are ok (I bought two more for a total of three); the front mesh covers that go over each bay don't line up that well either. It's all just "ok", not in the same league as the Lian Li.
However, the RC-810 does run a system a little quieter (those Cooler Master fans are great, I think around 70CFM or so and maybe 26 dB). I'd also say that it is cooler than the Lian Li (though I don't know how much).
Overall, the PC-V1200B is a beautiful case (and my old rig was also in a PC-70).