I recently spoke to a fellow Logos user only to find out ... he is still using L3 
The 100 new features page might help those who have not yet made the leap [or, those who HAVE L4 but rarely use it because they are so used to L3].
http://www.logos.com/4/newfeatures
However, the bottom of the "newfeatures" page shows the date 11/25/2009. There have been some GREAT new features added/enriched since then.
Just saying. 