From the Partimage website:

Partimage is a Linux utility which saves partitions having a supported filesystem to an image file. Most Linux and Windows filesystems are supported. The image file can be compressed with the gzip / bzip2 programs to save disk space, and they can be splitted into multiple files to be copied on CDs / DVDs, ...

And, yes, it's open source and part of the Ubuntu APT repository.

Since it's so easy for me to reinstall Ubuntu, I don't think I actually need Partimage for that. But I did need it, though, for my Windows XP partition. XP was a pain to install, and since it's prone to viruses and such, I felt I needed a quick way to restore XP. Partimage fits the bill.

Following are some screenshots of Partimage. On the whole, really very intuitive to use.

Doubly interesting is the network backup / restore function. According to the web site:

Partitions can also be saved across the network since version 0.6.0 using the partimage network support, or using Samba / NFS.

On the downside, I haven't had time to test the restore function, nor do I think I want to. Till then, I'll just keep my fingers crossed.