Apparently Inscription is not working as intended, so come Cat it's getting overhauled. We'll be getting medium glyphs, and once you learn a glyph you can always switch back to it without purchasing a new one. Hopefully this will make glyphing less of a "set it and forget it" thing. Personally, I rarely switch glyphs and I don't really know anyone who does. Granted this will really affect the glyph market, but since I make Darkmoon cards and vellums for gold, not glyphs, I don't care overmuch.
I do also like the idea of medium glyphs being sort of vanity items. So I figured I'd come up with a few ideas....
Glyph of Power Word:Shield Rabbit(turtle, gnome, belf, penguin, whatever)-> Your pw:s now has a 40% chance to turn the target into a rabbit(turtle, gnome, belf, penguin,ect). Change is cosmetic only and lasts 60 seconds. I like this idea mostly because it would be amusing without being game-breaking. Plus I like turning people into rabbits. Perhaps each healing spec could have a version of this, just so everyone's in on the fun. And no, this has nothing to do with my delight in putting gnomes in bubbles. Really.
Glyph of Life Grip: Color Change-> Your life grip will now change the target's color, to indicate they were an idiot and stood in the bad stuff.
Glyph of Spirit of Redemption: Sex Change-> The sex of your spirit of redemption is now male. I'd also like to see a version of this for warlock's demon form, allowing it to be female.
Glyph of Incubus-> Instead of summoning a succubus, you summon an incubus (male version of a succubus).
Glyph of Tree-> Your tree form no longer has a cooldown (for the broccoli-lovers who want to keep their form)
Glyph of Not A Crit Chicken-> Your boomkin form is now a buff that does not actually change your form.
Glyph of "You're out of range you idiot"-> When anyone in your group gets out of range of your beneficial spells, they immediately turn fuchsia, and will not return to normal until they are back within your range. Great for "go go go" tanks and dps. Does not work in battlegrounds. (And should probably only work on your group in a raid).
Glyph of Armor Change-> This glyph would allow you to wear one armor set while looking like you're wearing another. Both armor sets must be set up in the Outfitter thing, and you must have both sets in your bags. So those of you who thought Tier 1 was the most awesome thing ever could wander around looking like you're wearing it. Or you could tank Deathwing looking like you're wearing a lovely black dress. This is one I really really want.
Glyph of "crap, I wasted Heroism/bloodlust"->Once a week you can reset your heroism/bloodlust. This also removes the debuff from everyone in your raid.