It is not important to hold a number of different funds in each category, as it would be if you were holding individual stocks. Investing in two funds that are similar will not diminish risk. It's true that diversification among types of funds decreases risk, but this is true only if the portfolio has diverse components, and investing in two funds of similar type does not produce this diversity. The SmartMoney site is a good source for information on the performance of particular funds. They have loads of information on every fund, and allow you to x-ray your funds to see where the overlaps are.
Some investors buy the hot performers each year, but never sell any of their prior fund investments.
After several years, they have a complicated mishmash of overlapping funds that are difficult to monitor. Some are performing well, and some enjoyed only a brief time in the spotlight before they faded. If you find a new fund you want to buy, make sure it fits your portfolio's objectives. Limit the number of funds you own . That way, you will be forced to week out the poor performers before you invest in a new fund.