I'm not sure it's that useful in blitz play - I've heard endgame play is suffering amongst the younger generation because of this - and the fact you can no longer adjourn games means they get played faster as well.
I just feel like I can make better decisions in the middlegame knowing the endgame - here's two examples
I recently played a live game (Scotch but this is techincally a Ruy Lopez ending) where I strove like hell to get this position. Why? - Cause it's won for white - I can even beat Houdini with it now - unfortunately, I had to make a trade that compromised my kingside position but that's what happens when you play 500 points above your fighting weight

- but my middlegame decisions were motivated by an ending I KNEW unequivocally was winning for white - (for more on this ending - go to
http://www.chessvideos.tv/forum/viewtopic.php?t=9219 - he does an incredible job of explaining it)
ending number 2 - fighthing a guy 300 points above my weight class, I blew this ending in time trouble
as white, I picked up his passed pawn at the expense of my g2 pawn - but even then if I had played f4! instead of Kf5, I'd have been able to either trap his king on the h file with opposition or else outflank him to the h1 square, which would have been a draw. We all know about blocking a rook pawn by camping on the queening square, but we forget sometimes that we can have his king serve the same purpose - bet I remember better next time
Now I take positions like these, generate them in Fritz, and replay them so I don't blow them next time
here's a couple more positions I took draws on with black but they were easy wins provided I have 5 min left on the clock - (I'm usually down to about two though - doh) - actually I'm still trying to master the first one but if I can beat Houdini and Rybka and Fritz, then I know I'm golden against a human -
I think tactics and endgame play are much more important than opening study - at least till about 1800
RB