The "experimental" caution, as you might surmise, means not all features will work. For example, in Snow Leopard, there is no USB support, and Parallels notes there is no shared networking support.
Parallels has been running a competitive race against VMware Fusion as each software solution tries to out-feature and outperform the other.
The Parallels update can be downloaded at this link, or you can select "check for updates" from the Parallels application help menu.
A complete list of the enhancements in this build can be found here. Some users are reporting faster performance and some improvements with use of peripherals.