Temporary Root, for those who don’t know, is essentially getting root-user permissions on demand, or on boot. It differs from “permaRoot” in that with “tempRoot” every time you reboot you lose your root permissions, with “permaRoot” they’re permanent. To work around that, app developers have added into their “tempRoot” apps the ability to run at startup, essentially re-rooting your phone as soon as it boots up.
There are some draw backs (not being able install custom ROMs, for example), but with tempRoot you can typically perform the majority of commands that require having root permissions (such as removing all that bloatware that came pre-installed on your phone).
The HTC EVO Shift 4G has reportedly gotten temproot via VISIONary soon from the Unrevoked team’s “one-click root”.
The VISIONary app is no longer available in the Android Market, but can be obtained from Modaco.