I use k-7 for weddings. But the "look" from the camera was so much different than my other cameras that it took me a while to figure out how to process all my images so it looked like a cohesive set for an album.
Now that I am used to it this is my favorite camera. I use it primarily with DA*16-50, 43mm and DA*200mm. The increased focus accuracy is the biggest improvement for me. I now have to make a mental note and flip the camera to manual focus when I'm shooting my K20d in the dark (i.e. first dance) or I'll drive myself crazy waiting for it to lock focus.
I've used it for some video at weddings too. The still photos in this wedding came from a mix of Canon 5d, Canon 30d, Canon 1dmkIII and Pentax k-7 while the video was taken by a Canon HD video camera (I don't know what model) and the Pentax k-7 (with 16-50 mounted)
Wood's Blog Fusion Wedding Video
My only difficulty with my Pentax setup for weddings right now is getting a fast-wide lens. I really need the 31mm Ltd for church weddings but I do so few church weddings that I'm having a hard time justifying the cost. I've got a job this summer that just may push me over the edge though. I took a test shot in the church last week and the exposure was ISO 3200, F2.8, 1/20sec. So if I get the 31mm for my pentax I will probably shoot my Canon 1dmkIII with the 135mm F2 and the Pentax k-7 with 31mm F1.8. I'm not sure if the K20D will be invited to that wedding or not