Might have been this article:
http://lwn.net/Articles/525459/It's worth understanding the idea of mixing in entropy, and optionally accounting for it. It means your RNG can accept good or mediocre sources of randomness without losing any more randomness than necessary. So using uninitialised memory, or a MAC address, need not be a sin.
I'm pretty sure I've read somewhere, in a forensic context, that RAM has a tendency to power up in the state it's been in if it was in that state for long enough. That is, if you save a static password in the same location for years in your router, and then sell it, someone has a better than evens chance of guessing each bit.
Finally, I think it's pretty likely that a RAM would have a back bias generator, which is a good reason for it to need some warm up time. I can't quite see why it should be necessary to wait for five times as long as the spec though: what's a spec for?
Good story Jeff!
Cheers
Ed