Good idea / bad idea? Usually rock my L glass but have thought about adding a super-zoom to the collection, maybe even a 28-300. Used to have the Tammy 18-270 and I liked it, but I have considered the 28-300 because I'm on a full-frame sensor now.
I typically use a 5D, 540ez and a combination of a Canon 20-35 f3.5-4.5, 50/1.8 Mk.I and for couple portraits the 70-200 f4L IS. The setup works but changing lenses in the middle of a shot and carrying two or three of them around drunk people is getting old.

