If you're only after certain apps from Unstable, you might prefer using apt pinning (http://jaqque.sbih.org/kplug/apt-pinning.html
). That way, you're able selectively upgrade only those specific apps without needlessly jeopardizing the stability of the rest of the system.
Regardless of whether you choose a partial or wholesale move to Unstable, be sure that apt-listbugs is one of the first things you install when you do so. Each time you upgrade, this will warn you if a package has serious bugs filed against it, at which point you check out the bug for yourself to see if it applies to you before upgrading the package (or not). This should shield you from the vast majority of the breakage.