I am one of those weird people who prefers my archive files to have different icons based on type. Iconographically (three cheers for making up new words!) speaking, there's something wrong in my mind with having my zip files share the same icon as my rar files. I like being able to tell at a glance if something is a rar or a zip. Why? Personal quirk, I guess. No real utility in knowing, I suppose, but back when I first started using PowerArchiver it was the only archiver app that could do it. Nowadays, others do, but I stick with what I know best.
Graphically speaking, it's one of the most visually appealing programs of its type available. Turning on Explorer View and using the modern ribbon interface makes for a very efficient UI and it handles more file types than most of its competitors.
For the security conscious, it's very versatile in its encryption capabilities and offers an array of choices of encryption methods.
Their forums are great & you'll get the same great answers for your questions whether you bought the program or not.
Offhand, I can't remember if it's limited to the Pro version or not, but your purchase price also grants you lifetime licenses to their excellent Outlook plug-in and a command-line version of the program that can handle just as many archive types as the GUI-based program.
One little feature that you'd think wouldn't make a difference that has really improved my productivity is in the last few versions they added MRU support for the "Extract to..." context menu command. I extract lots of files to the same few directories over and over so this has been a real time-saver for me.
I won a free license for WinRAR (Thanks, DonationCoder!) and I use that for all my archiving needs, even after getting that free I still bought a license for PowerArchiver Pro for all my unarchiving needs. (I took advantage of their crazy 80% off upgrade to the Pro version before they raised their prices.)