If you are paying private insurance on your current mortgage, refinancing may allow you to do away with this unnecessary expense.
If there are only a few years left on your current loan, it's no use refinancing with a long term loan. You may need extra cash but with a long term loan, you'll end up paying more for the entire loan term.
If you are refinancing from one ARM to another, check the initial rate and the fully-indexed rate. Also ask about the rate adjustments you might face over the term of the loan.
Stick with a simple loan. It is easier to understand and less likely to get you into trouble. Adjustable-rate mortgages may seem like a way to get a bigger house now or to keep more money now, but when the rates adjust you can get into trouble. Avoid anything with a balloon payment. Just choose a simple 30-year mortgage you can easily afford.