...I decided to tackle problem I recently found out about in fwbackups. If there is a large amount of stdout or stderr output in a short amount of time from the backup subprocesses, fwbackups hangs. That level of output should never normally happen while backing up user files, but if /proc or /dev is included in a backup for example then it could trigger the problem.
After 8 hours  of backup benchmarks, I've concluded that not only is python's tarfile module horrendously slow (with gzip compression enabled, it is consistently two times slower than calling "tar" from the command line as a subprocess) but that I unfortunately have to reverse the feature I added in 1.43.3rc3 that adds the display of the file currently being backed up in the GUI. Sorry in advance, but it was the only way to keep both performance and prevent fwbackups from hanging mid-backup in certain situations.
 which as it so happens, is also how many hours there are in the first season of How I Met your Mother. It's a hilarious show!