To join the chorus, I subscribe for the Compendium.
I play online using a VTT, and I keep the Compendium open while I'm DM'ing. It is a tremendous benefit to be able to reference Monsters, PC Powers, Rules, etc. with a few keystrokes.
I find the quality of articles in Dungeon and Dragon to be satisfactory. Some articles are stinkers, but (IMO) that's always been the case. However, I dislike the way the articles are presented on the website. Depending on when or how frequently the site is updated, an article can fall off the main page fairly quickly. I don't always download and read the articles immediately, and once they drop off the front page, I'm unlikely to ever come back to them.
I'd like to see WotC go to a blog-style format with its website, where content remained on the front page a lot longer.