I've been using Logos DLS for 5 the past years on the PC platform and I totally love it. I can't imagine being a pastor or serious student of the Scriptures and not having this software at my fingertips. I also just upgraded to the Silver Scholars edition and unlocked hundreds of new volumes for my digital library. I now have literally thousands of reference works on my laptop that I use everyday for sermon preparation and Bible study.
If you are a pastor or Bible college / seminary student, I would strongly recommend you purchase the Logos digital library system. If I was a carpenter, I would have the best nail guns, circular saws and digital levels that money could buy. But since I'm a pastor, I'll stick to my digital library and for my money - Logos from Libronix is the way to go.