Hey yeah GUEST! I use the major 7th barre all the time. On great song I know has you going from G up to Ebmaj7, down to Bbmaj7, back to Bbmaj7, etc. Crow, it's easy to sneak them in. You play a Cmaj7, and very very quickly hammer on the C note and then play the C chord, barely noticable! Also, some major 7ths don't rings as well as others, like an open Emaj7 is kinda murky, so you can fit it in places!

--Mbo