a slick and a mtb tire
 

right now the mtb tire is on the back, and it feels like i am crawling. would it be faster to put it on front and the slick on the back?

and what do ya'll think of those thorn-proof tubes? after 5 flats in 8 days i had to take off my rear slick, i was spending to much time fixing flats!!! my tire wasn't worn down and there wasn't anything stuck in the tire that was making it repeatedly go flat. It must have just been terrible luck.

GQ

It will probably feel faster, but front knobbies do wash out(in turns) easier than slicks on pavement
The tubes do work but are heavy
Are you SURE there is nothing in the tire? Mark the stem location on the tire, pull the tube, inflate it, find the hole in the tube, using the mark on the tire and the valve stem as a reference go around to that spot on the tire. If the hole is on the inside of the tube go get a velox or other cloth strip rim liner and replace the old one. If there are two holes right next to each other then you are pinch flatting and you need to use more air or dodge more stuff.

how about using two slicks?

you may want to look at stans no tubes rather than heavier tubes. they are heavy and really increase your rolling resistance. A buddy of mine had them and couldnt believe the difference in goin back to a standard tube. You could look into an armadillo tire as well. some of the people on here who run them have had great luck with them. Specialized makes the "armadillos".

I have had good luck with Armadillos on my MTB. No flats in over a year. I got a couple miles an hour out of going to slicks.

Thorn Tubes
 

Thorn tubes are heavy. I have two nearly identical Trek 4300 MTB's. One has thorn tubes with slime, the other has regular tube with slime. The bike with the Thorny feels much "heavier" on the road and also in my hands.

The funny thing is that I really notice very little difference in speed or times between the two bikes. (both bikes have cateye mity 3) If anything I think I may be a little faster on the bike with the Thorns. Keep in mind that where I ride, I have NO hills to speak of. If I was humping up and down hills i bet it would be a different story.

Most people also suggest running a tire with more tread on the front since it is better to have the back wheel slip than the front. The crash is usually less severe this way. So i would suggest putting the slick on the back.

More tread on the front would be good for off road. If you are talking road slicks, the knobby on the front can make that wash out first.

If you're getting repeated punctures, I'm betting you have something stuck in your tire. I've had a couple of unfortunate incidents when I wasn't able to find the glass or thorn or whatever, but a new tire sure solved my problem.