Now that Squeeze has been released, we (the pkg-xfce group) are in the process of uploading 4.8 to Debian. And we are uploading it to experimental for good reasons.
What does this mean for you? That you should *not* upgrade to Xfce 4.8. Not all packages will be upgraded, and mixing 4.6 and 4.8 is a bad idea. We don't know yet what will happen (and that's the whole point of uploading to experimental), and it seems that there are issues indeed.