> So what kind of performance can you get from Cassandra?
~10k ops/second per quad-core node. Scales roughly linearly w/ node and core counts. ("Roughly" means, obviously there is network overhead as you move from single node to multiple, that kind of thing.)
> How big can the values be?
2 GB, although you probably don't want to max that out.
Cassandra is mostly used for smaller pieces of data, although I do know at least one person using it as an S3 replacement by chunking files into 64MB chunks; each file is one row consisting of columns that each contain one such chunk.
> I was thinking of using it as a backend for a mail system.
