Damn thermometer up in the closet still says low/mid 60's though. *sigh*
I've been reading this forum, and I don't see why so many people have made a huge deal that you bottle condition ABOVE 70F. While this is optimal, it is not the only way you can do it. I don't have enough room in my apartment where it gets to 70+ for the 3-4 cases I have conditioning at any one time. I keep a few in the kitchen cabinet, and the rest in my closet in my room where it is at 68F at the highest point. It gets colder than this, and I still have great carbonation on my beer. You can bottle condition at any temperature that the yeast will survive at, but it will just take additional time the colder it gets. I've had overcarbonated beer conditioning at 60-65F. This also depends on the yeast, some can even go down to low 50s, which is cellar temp, and a LOT of people condition in their cellars.
No one has seemed to mention the fact that if you are frustrated with your levels of carbonation, you might want to add more priming solution, and raise the temp of the conditioning, that this can be a bad idea as well. The higher temps will cause more bottle bombs if the yeast eat the priming solution, in addition to the sugar leftover in the beer, too fast, at too high of a temp.
I am relly suprised that no one has mentioned the more important factor in carbonation YEAST VIABILITY! This is by far the most important factor in producing a carbonated beer. You need healthy yeast in your bottles to carbonate, if you don't have enough, it can take an extremely long time, or not happen at all. Many people want a very clear beer, so they reduce the amount of yeast that goes into the bottle. I make sure to suck some yeast up into my bottling bucket, it will settle out of the bottle during conditioning, and you can leave it on the bottom when you pour.
If your beer has a clean sweetness, there is a good chance its the priming sugar. In that case, you can remove the caps from the bottles, add a little dry yeast, and cap them again. See if this does the trick in a few weeks.
I don't want to disregard the higher temp of conditioning, but it isn't a must to have carbonated beer. Yeast however, IS a must.