Has anyone experimented with using a CD-R drive as a backup device?

CD-R media sells for $2/disc in Canada.  The disc holds >600MB.

Even though it may be write-once, this is incredibly cheap.  Is it reliable?

I'm thinking of going this route.  Software-wise, I'd need something that
can stage an incremental backup onto a holding disk, convert it to ISO9660
format, then blast it to a single session of a multi-session CD.  The holding
disk is required, since the actual burning of the CD must be done in real-
time - you cannot stop writing or let your data stream underrun once the
write operation is in progress.

Is there a limit to the number of sessions on a multi-session CD?

Does backup software of this nature exist anywhere?