There's been a bit of buzz around the Apple community about HDCP, and why it's terrible. Specifically, it looks like the new, DisplayPort-bearing Macs are HDCP-capable, which in turn means that some content you buy legitimately from the iTunes store won't play on external monitors unless they're also HDCP-compatible. As this thread on the Apple support forums indicates, the list of now nonfunctional displays include any non-HDCP-enabled Apple displays -- in other words, any Apple Cinema Display sold before last month.
This is, in a word, terrible. The larger Apple Cinema Displays are multi-thousand-dollar investments that by rights should last years, and many of them were purchased for precisely the purpose of watching movies; it's unreasonable to require users to buy a brand new one to enjoy movies that they bought legitimately on a new laptop. The arguments about DRM have been hashed and rehashed, so I won't rage further about it here, but I do think it's odd that Apple hasn't even bothered to put out a "Sorry, the studios require this stuff, we had no choice" statement. Maybe they're going to fix it? Here's hoping.