Two tanks of gas ago, I had a quarter of a tank, filled it and the gas guage when right to the bottom and my "gas light" came on. About an hour later, I noticed it was where it should be. I thought it was just a fluke. With my last fill up, the guage stayed where it was (at about 1/8 of a tank)and I watched as it very slowly went up to full. This took about a half hour. Is this OK or does it mean that my guage should be replaced?

Sandy, sometimes when its real cold you may have a period when your gas gauge takes a while to "catch up" to the actual level. Since it likely isn't cold where you are right now I would suspect that the sending unit in the tank may be faulty. These issues vary between car makers so you should have it checked out. In the meantime you should just reset your trip odometer each time you fill up to make sure that when you get close to the maximum range of your car on one tank that you fill up again. That is normally about 300 miles for most cars, just to mae sure you don't run out of gas.