Once again, there is the "right way", and there is the "get by making it work on a budget way".
The "right way" - which in this case is using proper DMX cabling - is the right way for a reason. You will have less problems, you will be able to rely on your rig working like it's supposed to, and you won't be wasting money in the long run on temporary solutions. If you can afford it, get the proper cables.
However, the "get by....budget way" does have it's place. You will not damage the cables at all by running mic cables. Most likely (and that's the crux - most likely, but no guarantee) if you are running relatively short lines and few fixtures you will get by just fine with mic cables (especially good twisted pair ones).
On the for-what-its-worth front: I run upwards of 46 fixtures, with a total of about 180-200 feet of cabling and I use mic cables. This rig has seen a LOT of use in a lot of different venues, and I've never had any problems (at least none that were cable related). I didn't plan to do it this way. My rig has grown bit by bit, and when it started I had mic cables available so I used them, telling myself that I would switch to "proper" DMX cabling in the future. It always seemed that whenever I added a new fixture or two, I had a mic cable handy and opted to use that "just for now" rather than buy something new. So after a while I found myself running a somewhat extensive rig, all with the "wrong" cables. BUT....it's all working so the incentive to go out and spend a big chunk of change to fix something that ain't broke is not exactly strong.
So, don't mickey-mouse it if you can afford not to. But don't completely discount the concept either.
One thing though...DO absolutely use a terminator at the end of your line. This will make a much bigger difference to the performance of your system than using proper cabling.