No, it's not equvialnt to either MS's GUID or the original UUID features. That has provisions for setting the clock back (e.g. daylight-savings time or corrections if you notice it's fast) while you could get the same time; The process ID will be the same for the life of the program and could certainly be the same on different machines running at the same time; a UUID includes the machine's MAC address and following the algorithm will always produce unique results.

How random is rand()? Assuming it's 32 bits, that's the majority of your effect. The $$ will protect against multiple processes calling this at the same time on the same box, if Time::HiRes didn't already do that (e.g. multiple processors).

I think it's a little better than a random number alone, but not a sure thing. It's longer than it needs to be for the amount of uniqueness it offers. I'm against formatting it like a GUID, since I like to think that if it looks like a GUID it must have been generated using the common algorithm.

You can find the source code for UUID's in the DCE code.

—John