I know it's on the "when I feel like it" list, but I'm another one who would love a multisession ability.
Presently I use CDBurnerXP for my project backups. Frequently I have just 20-50Mb or so of data in a project but need to keep an isolated backup of the project history. Having to use a new CD each time and end up with multiple CD's with almost nothing on them for the one project just doesn't work.
Here's hoping it'll come sooner rather than later.