On the whole (pun intended), I'd have to agree with most of these replies. I might take exception with iceyflame - because a hole lets air out, it reduces the resonance of the drum.
Regardless of all that, it IS possible to get a good sound without a hole... however it often requires lots of time, energy, and sometimes dual-micing to get the sound you want. If you're ok with very little definition in the sound, mic the resonant head - you'll get a low, muddy thud. Probably won't sound very good. On the other hand, if you mic the batter head, you'll get a good bit of click, but not much resonance, depending somewhat on how you play (do you leave the beater against the head at all, or does it come right off?) and where the mic is.
The easiest way to get a good sound with one mic is really to cut a hole. How big of one depends on how much resonance you want your drum to have. If you like it really dry, you could cut up to a 6" hole for the mic (or leave the front head off...). Really wet and resonant, down to a 3". Personally, I'm a big fan of a 4" hole, off to the side and down a bit, with a good bit of padding inside. You can control the resonance with the padding.
I personally love the way my kick sounds right now - I've got a pretty heavy batter head, a wood beater, a single-ply resonant with a dampening ring and a 4" hole, and then some foam inside. I also use a D6, and just shove the thing in about halfway - almost always sounds fantastic. Sometimes I'll just throw the mic on the foam inside if I don't feel like fooling with the stand. I tune the batter head very loosely, just tight enough to get the distortion out of the head, and then tune the resonant head to a nice low kick sound.
Just my two cents... try different things, start with a SMALLER hole and work towards bigger if you want. To me, bass drums are pretty easy to tune, at least compared to the rest of the drums. You'll find a sound you like with a hole - don't worry.
