It was pretty obvious that Ricky Gervais had complete control over how the cameo would be approached. Instead of it being some sort of ridiculously inane plot revolving around a guest appearance a la Chris Martin on When the Whistle Blows, it was an unexplained, coincidental crossing of paths.
It felt very rewarding as a fan of both shows to see a bridge between the two. It was as if Gervais gave the official stamp of approval, as if to say that he validated the show and its fans.
I would have liked to see more of David Brent; however, I always respect when a performer can leave me wanting more. It is much more appealing than when an audience wishes there had been less.
My only real complaint is that, as great as the rest of the episode was, it paled in comparison to its first few minutes. After such an ostentatious opening, I was unable to give the rest of the episode my full attention, as I was still processing what I had just seen.