How deterministic Are .Net GUIDs?

Question

Yesterday I asked Are GUIDs generated on Windows 2003 safe to use as session IDs? and the answer combined with combined with this article GUIDs are globally unique, but substrin

Answer 1

It's not a complete answer, but I can tell you that the 13th hex digit is always 4 because it denotes the version of the algorithm used to generate the GUID (id est, v4); also, and I quote Wikipedia:

Cryptanalysis of the WinAPI GUID generator shows that, since the sequence of V4 GUIDs is pseudo-random, given the initial state one can predict up to the next 250 000 GUIDs returned by the function UuidCreate. This is why GUIDs should not be used in cryptography, e.g., as random keys.

The rest of the article, and its references: http://en.wikipedia.org/wiki/Guid

--Edit--

From a security standpoint, I'd suggest that you generate your session ID however you feel like, then cryptographically sign it; that way you can pack in whatever information you want and then just slap a signature on the end - the possible issue being the tradeoff between the size/strength of your key and the resulting size of the cookie. GUIDs are useful as IDs, but I'd only rely on a dedicated cryptographic technique for security.