If you are being paranoid you might prefer to wait for ever for a good random value instead of accepting something you are even fractionally less sure of.
Though practically speaking, that would probably not be acceptable in most (if not all) circumstances.
If you are that paranoid then there are inexpensive true-RNGs out there (free in fact, if your CPU or other chipsets have one that is easily accessible) which can provide enough bits for all but the larger bulk requirements (i.e. generating many keys in a short space of time). You can either use one of them specifically for the process(es) that definitely wants absolutely true random of feed its output into the standard entropy pool.
