Is ISAAC considered secure as a cryptographic random number generator? The ISAAC site claims it is secure, but I wasn't aware of any trusted 3rd party sources that verified its security.
I had a short look at the page - it contains only some implementations, no specification.

The page ISAAC and RC4 from the same author contains some theoretical elaboration about ISAAC and its relatives IA and IBAA, but I'm not sure if this can be called specification.

Non-existence of a formal specification is a major drawback for anything which claims to be a serious cryptographic algorithm, and might be the deciding reason that nobody really looked at the security of this primitive.

So my recommendation would be to use other, better documented algorithms instead, if security is of importance (and not only speed).