TeX Live 2012 is available online now. It will be sent on DVD to members of most TeX user groups later this summer (barring unknowable production and mailing delays).
You can acquire TeX Live in many ways. For typical use, we recommend the first two:
The last general update of packages and programs for the DVD was made around 10 June 2012. However, we will be continuously updating packages in TL as they are released to CTAN. Post-installation updates are done with the tlmgr program. tlmgr also provides many other TeX installation options and features, explained in the tlmgr documentation.
Although it is possible to update continuously, it is not necessary or even recommended. The set of packages and programs that were included in the official release will most likely suffice unless you know you specifically need updates made since then. That set is also the only one which gets tested as a coherent release.
Older releases of TeX Live are available. You might find one useful if you need a release of particular vintage. There's no problem with having multiple versions of TL installed (in different directories); in fact, the default directory structure is arranged to facilitate this. After installation, just set your PATH accordingly.