I use my iLiad for almost all paper keeping these days. I scan bills, mail, notices, place them on my iLiad. I do school work on my iLiad, and any documents related to work (web application programmer) goes on my iLiad, so obviously I am in a bit more need for some memory.
1GB is a fair amount though, even for my use, over the last 2 months I have had the device I have only used about 100 GB of storage.
Originally I was using the SD slot, but found this to actually be just a little unstable. Sometimes the content listener wouldn't save or didn't list contents on the memory card.
I switched to CF and all my problems went away, not to mention the CF is generally faster for read/write operations (look at
http://www.robgalbraith.com for more info). And I did notice a definite performance increase when I switched to CF. I am now using a 2Gb Sandisk Extreme III CF card.