The cavalry was used very successfully, it's units achieved a lot of victories, maybe because all men in cavalry were physicaly tough? They used horses only as a transport and when they had to fight, they gave all horses to one or two special men, who took them to safe place, and only then cavalry attacked. So, basically, they fought as normal infantry.
I can't get you any facts about cavalry charges in ww2, but if there were some, they would be an attack at unknowing enemy. Maybe you remember how one of the naci's panzer generals (Guderian, i think) wrote about polish cavalry attack: he wrote, that those "barbarians" attacked them on horses with swords. He even wrote that they tried to cut panzer's armor this way. Of course, it was a big pile of bull****. In fact, that polish unit found german camp, and fashist's didn't know anything about them. So they decided to attack mounted - it's quite difficult, you know, to use your kar, when your enemy is in 20 meters before you and has a horse (not only physically, but also psyhologically. That's why they have mounted police nowadays). The attack was very successful - a lot of fritzs died in that slaughter, but then few panzers arrived and started to shoot with mgs. Polish cavalry fell back, they had some killed. But they didn't attack panzers, they attacked unknowing infantry and were successful.
I'll try to search some more about soviet cavalry, if you want.