I am interested in this software, but would like to know if anyone here uses it and can answer two questions for me.
1. Does Directory Opus have any form of DRM attached to it?
2. How do you like it as a replacement to Windows Explorer?
Thanks

Yes.
What is Windows Explorer?
But seriously, best thing since sticks and stones.

Elucidate please...

When You buy Opus, You get the software, and a license.
The license is checked every time DOpus checks for updates. I don't remember how long is the license valid, You'd have to check their info/forums, they have a neat community there, making and sharing scripts, buttons, exchanging ideas, helping out making own modifications etc.
Anyhow, the license is time based and/or version based, though i don't remember if it's for a full version upgrade [like 1.13-2.13], or just until the next major release [1.13-2.00]. Either way You don't have to upgrade, and use the latest version You have forever. Again, You should check their forums.
A word of warning, though DOpus works out of the box, it's kinda like Foobar2000, the more you tweak, the better the experience.