First, slightly off-topic self-promotion:

There's been a lot of talk recently about how iPhone backups contain a full history of everywhere you've been. There has even been apps to visualise this.

I took it 1 step further, and proudly present http://markolson.github.com/js-sqlite-map-thing/ which is 100% client-side javascript to parse the sqlite db files in you backup and visualise you tracking history.

Second, the compression angle:

In doing this I met the binary sqlite btree db format for the first time. And I wondered how well conventional compressors do modelling btree dbs, how well delta updates compute and whether there are any specialised compressors and differs for db files?