Despite the fact that I haven't created a RL deck in ages, I still have about 19 of them still constructed and in nice little boxes (some as old as Revised, and some boxes as "New" as Tempest). The reason for this was I would play insanely long sessions w/ my friends every Wed nights and if everyone just used the same decks over and over it would get really old fast, so each of us had about 8-12 decks. Now, you might be saying that 12 is less than 18. Well, I had to create six new decks after the release of one of my favourite cards: Coat of Arms. Even w/o all of the cool tribal stuff from Onslaught Block you could still make some pretty cool theme decks w/ Merfolk, Wizards (old school B/U), Spikes, and Thallids (that's right: Thallids). I also made the necessary Goblin deck and a black and white Knight deck.
Now, on MTGO, I have only one deck that I used regularly that was modified three ways (Emperor strong flank, Emperor weak flank, and straight duel). Since I can't afford an extensive collection of online cards, this probably won't change anytime soon - which suits me fine since I'm not expecting to have a decent connection until next month and even then, I shouldn't have the time to dedicate to serious casual online play.
-Ferret
"Serious Casual?"