I signed up a couple of weeks back. Took 5 or 6 hours for a reply in my welcome post. That's when I lost interest. DP is like an IM, SP is like snail mail. Having said that, the main site I use a lot for PHP inspiration. But the forum didn't impress me much. It's a different crowd anyway - more web development rather than web marketing.
Sitepoint used to have good link exchanges but you must pay for you to have an exchange of links. I liked DP more because DP is open for visitors, I became a visitor in SP and nobody cares to answer my concern.