The prime rate is incredibly low. Pretty soon now, it'll have to start increasing again. Depending on how fast it goes up, it might not have too bad a slowing effect on the economy. One of the worst case scenarios would be for a burst in the housing market bubble, especially in places like San Diego where home prices have gone up about 20% a year for the past couple years. A cooling of the housing market would be tolerable, but if housing prices went the way of the dot-bomb stocks, it'd be a disaster.

Contrary to what some people believe, low interest rates aren't good for everyone. Those living on fixed incomes who often keep their money in money funds, CDs, and other safe investments tied to the prime rate have been hurt very badly by the low rates for the last 3 years. I've seen CDs in the past couple years that only offer an interest rate of less than 2%, less than the inflation rate. To add insult to injury, they get taxed on that pitiful interest, too, meaning their "safe" investment is guaranteed to lose money in real value terms.