Does this work with the AirPort dynamic global hostname? I put my username and password in, but since my IP didn't change since I signed up I couldn't see if it was working right.
IPv6 mobile address portability attempts to keep your IPv6 address constant as you move around different wireless access points or LANs within a company or ISP network. It doesn't provide a globally static address or way to provide a static hostname.
Even with a static or mostly static IPv6 address the ability to have a dual stack dynamic hostname where both the v4 (that changes a lot) and the v6 (which might change less) is still useful. It is also obviously useful as you roam between office and home and such and want to keep a hostname constant.
Mobile IP in IPv6 is very much meant to keep your stable, global address working while you roam around the global Internet.
The route optimization mechanism means your packets can travel directly between the mobile node's care-of address and the other guy if they both support MIP, so no need to be even on the same continent.
Sadly MIP is mostly dead, though there seems to be a somewhat up to date (2013) Linux impl of Mobile IP v6 and NEMO for IPv4 here: http://umip.org/
My impression is that it was kind of overshadowed by IETF's efforts to make an architecturally pretty fix to the whole locator-vs-ID thing. This is the work leading to the LISP protocol. You can now find papers from Facebook, Cisco, etc advocating its deployment. Hopefully it will get popular at some point.