While the prospectus is packed with great information, it shouldn't be your sole source of data on a fund. A fund's Statement of Additional Information (SAI) contains more great tidbits about the fund's inner workings. You'll generally have to request this document by calling the fund company: Funds send out prospectuses and annual reports as a matter of routine, but SAIs are often considered second-tier documents
Fund families may consider SAIs secondary, but these statements usually provide far more detail than the prospectus about what the fund can and cannot invest in. Further, this document usually identifies just who represents your interests on the fund's board of directors and just how much you pay them for their efforts and how much these directors own of the fund.
Finally, you can find more details about your fund's expenses here. Shareholders in CGM Focus CGMFX wouldn't know they shelled out $24.2 million in brokerage fees in 2010 unless they had read the fund's SAI. SAIs also break down where 12b-1 fees go, if the fund charges them. (These are fees that the fund can use for marketing, rewarding brokers, and attracting more investors.) For example, Legg Mason Value Trust C (LMVTX) spent $25.3 million in connection with "share distribution and shareholder services," including broker compensation. It's your money; you should know where it's going.