First of all, thank you for your excellent work, I've been using BackupPC for a long time and it's awesome.
Now, here's my suggestion: create the option to allow N concurrent resources backup for a host. I take incremental backups for a server who stores more than 1TB (in different resources) and the rsync list building process takes most of the time (up to 20 hours) while the copy process takes only one or two hours. As my server is power enough to make those rsyncs at same time, the backup time will be reduced significatively.
My current solution is to sepparate the host in two hosts entries, with same IP and information but different resources, but even when it works, it's a little bit tricky.
Finally, I'm a developer (not an expert in Perl), but I would try to make it by myself if someone points me to the right part of the code.
Thanks in advance