I tried it for the first time last weekend. I haven't had much time for smoking lately, so I've been using the kettle almost exclusively with RO lump. I had picked up a bag of K-Comp a few weeks ago, and I found myself with a free Sunday afternoon and a couple of thawed racks of spares, so I decided to dust off the WSM and give the K-comp a spin.
I filled the charcoal ring to maybe a little more than half capacity, put about 10 lit briquettes in the center of them and let it come up to temp. I was able to maintain a pretty steady 230-240 dome temp for about 5 1/2 hours.
A couple of hours into the cook I put a fatty and some ABTs on the bottom rack for a couple of hours.
After the ribs came off I looked and the fuel most almost completely gone. A lot less ash than using regular K, and it seemed to me to be a little easier to manage temps than I've been able to do with lump. EDIT: [Disclaimer here - I was very careful this time out to start with less lit fuel than I have in the past, and I diligently monitored temps in order to slow down the rise in heat on the way up, so I may have been able to achieve the same level of control with lump - still learning!)
I didn't realize how much I missed cooking on the WSM - I'll be doing that again this weekend!