This appears to be an absolutely fantastic app - been using it since this morning and saving tons of disk space, so far without complication.
Having said that, the FAQs on the developers website is a bit FAQ-lite. Are there any types of files that shouldn't or can't be compressed? And why do some folders seem to take a very long time, whilst others compress very fast, unrelated to size? Is it better to compress folders individually or can you compress folders containing many others? Is the process reversible? If so, I can visualise a situation where previously compressed files might exceed disk space.
Perhaps a forum will spring up with answers to these kind of queries. In the meantime, though, it seems to be a wonderful utility in this era of ever-expanding hard disk needs!!