backwpup runs perfecly on my website now (I have still problems with the cron schedule, but that should not be of your concern).
However, I regularly receive the following message in my report file:
2013/01/26 10:36.57: [WARNUNG] ftp_nlist() [function.ftp-nlist]: Unable to create temporary file. Check permissions in temporary files directory.
As warning message I could savely ignore it, but I am curious: What is meant by the "temporary files directory" - where is that located or how is it named? Without this information I cannot check :- ).