[boost] Generating unique identifiers at compile-time

Meta-Programming, as used in Boost.MPL and others, allows to compute arbitrary values at compile-time, in a Turing-complete manner. However, something like generating unique identifiers at compile-time, which would be fairly useful, requires some kind of entropy source to create a random seed. One can maybe extract some entropy from macros such as __DATE__ and __TIME__, using both preprocessing and templates. Among you boosters, which are well known for your interesting in meta-programming, is there someone who ever tried to look into this?