I was able to contact someone on IRC who said they happened to have an early seed of OS X 10.6; here’s the info I was able to get from them before they went offline:
OS X 10.6 Pre-WWDC Secrets
Q: what’s different?
A: mostly just speed/stability, but the ui is going darker
Q: like iTunes?
Q: send me a screenshot plz
A: can’t it’s all marked
A: with user information
Q: [use an image editor to] blur out the parts with your info on it
A: it’s more advanced than that
Q:go into the guest account 🙂
A: they’ve thought of that
Q: and where’d you get it from
A: I can’t tell you that
Q: why can’t you tell me?
A: I can’t tell you why, but it has to do with the new ui
Q: what about the new ui?
then the person left. Seems interesting. Not very reliable, though