I'm trying to get a local up to date copy of my account, and am not having any success- the cPanel home directory backup will not give me a good copy (after trying many times- each give an unexpected end of archive error), and trying to ftp times out at about 1/2 done.
I have about 4.5 gb of data. *Might* a complete site backup work? I hate to do that on the server, as I know tar uses quite a bit of cpu power, and I'm afraid it would time out before downloading anyway.
Pulling my hair out.

Thanks Mitch- a bit of a story. I did the full backup (the first time I have ever tried that), and it went without a hitch, and downloaded fine.
But.... when I went to extract it, I got an error- just like the error I got for the home backup.
The nice thing about the full backup is that it emails an md5sum when done, and I compared that to the download- it came up the same.
So.... the problem was on my end. For whatever reason, my gui archive manager was giving errors and not completing, maybe because of the nested tar files.
I went "old school", and used command line gunzip, then tar to extract everything, and got a good backup.