I have three copies of WoW
First is for Retail where i operate on Argent Dawn - EU with 5 level 80s. I don't BG much unless it's to get something for roleplay
Second is for CotH where i hug all you awesome people!
Third is a permanent realm which will remain at patch 3.3 when Cataclysm is released incase i want to do any machininma set pre-cata.
I have two folders for CoTH and retail. I play on retail pretty much every day of the week and BG a fair bit. I'm more active on retail than CotH.
Two folders here, and as the above person. Play Retail rather daily nowadays, battlegrounds, dungeons, you name it.

Also tested my computer, and can run both WoW's at the same time, with 7 fps.. lol.
Edit: I'm on horde side of Skullcrusher, PVP realm. A troll 'mon.
Three copies of WoW, 3.3 for here, 1.12 for nostalgia purposes cause I miss my Vanilla RP's and I missed the awesome content ect, ect. The third unfortunately can not be publically discussed as of right now.
As far as servers go, mostly only two
Wyrmrest Accord- Daginae/Dieane
Shadow Council- Artimis/Daginaie(alexander IC) and formerly Dyane. Dyane was deleted as of last year, dumb mistake as she was my eldest and original character in WoW.
Unfortunatley, I do not have the money or really the want to return to the cesspool of retail right now.
I escaped retail. Im now safely here

Two installations for my laptop and desktop but I keep them on same version depending where I play. But I think I am done in retail, so I'll be back!