Dude you're awesome, not even an hour to enable m4v. Customer Service and Support Centers in general could learn a thing or two from you.
I've noticed that VLC media player plays almost all video files i throw at it (pretty impressive). When installing VLC the video file types it suggests to be associated with it are:
.asf
.avi
.divx
.dv
.flv
.gxf
.m1v
.m2v
.m2ts
.m4v
,mkv
.mov
.mp4
.mpeg
.mpeg1
.mpeg2
.mpeg4
.mpg
.mts
.mxf
.nuv
.ogg
.ogm
.ogv
.rmvb
.ts
.vob
.wmv
All of these are video filetypes even though some of these aren't commonly used for movies.
Maybe there's something in it worth adding. I've only seen maybe 2 .m4v movies in my life but here is someone who actually chooses to use .m4v on a regular basis.