Naomi,
Since most databases are highly compressible there stands to be some appreciable benefit from space compression. Last month at the SQL group meeting here a vendor was presenting a patented driver that claimed that their compression technology doesn't degrade over time the way the native SQL Server compression does.
>It still was an interesting read, wasn't? :) I wanted to reply immediately that the space would be re-used, but decided to double-check myself and started googling on the topic.