Here are some interesting sites describing the use of horses in WW1:
Horses in WW1
The Forgotten Army
It seems that, while cavalry were still considered the superior military units at the outset of the war, this very quickly changed with the onset of trench warfare, and that cavalry charges were rare after the charge at Mons in August 1914. Throughout the remainder of the war, horses were used mainly for transport. I doubt that they were commonly used on the Western Front for reconnaissance purposes, since trenches, barbed wire and craters would have rendered this difficult, although it's possible I suppose. I couldn't see any mention of that in the articles linked to above though.
I did, however, find the following piece, which indicates that Australian troops used light horse brigades for reconnaissance purposes:
THE 3RD LIGHT HORSE BRIGADE SCOUT GROUP WW1