Well, if properly ventilated and cooled, a wooden case shouldn't be much of a problem...
On a frame type like SpeedBump's, you can mount a series of 40mm fans on the bottom and a venting grill on top. You get your cooling, and natural thermodynamics (i.e. - "heat rises") can help out with the rest.
On yours, dman, all I can see from the build link is a front shot, but if that's an indication of the rest of your HTPC, then your issue might be non-fan ventilation. As in, I don't see any. Most computer cases have vents, grills, and such in there to assist in heat extraction and airflow.
If I may offer a suggestion on an improvement for the next go around: I like the scratch build, but I would have built the front, back, and sides as a framework to hold the components and then overlaid them with louvered slats (slanted to allow heat to travel upwards unimpeded), and the top would be slatted, perforated, mesh, or just not there. It would improve the cooling and add a little decorative flair to the HTPC.
Just my own thoughts.
Edited by TheMadProfessor - 8/13/13 at 7:59am