Bicycle tires will typically lose a bit of air over time, how much depends on the quality of the tube. I use Schwalbe tubes in my daily rider and can get away with only having to add air once every couple of weeks. I have an old cruiser that we keep here on the farm, it has WM Bell branded tubes in it, it needs air added at least once a week. When you replace a tube that has a pinhole leak (or larger) run a cotton ball around the inside of the tire first and see if it catches on anything. My curse has been the little pieces of wire from blown out truck tires, hard to see and hell on the fingers if you find one with your finger tip.
I don't like the slime, I had a blow out on a tire with a slime tube (came on the bike new) and it was a helluva mess to clean up. YMMV
Aaron
