HereBeDragons wrote:
I tend to run a 60 card deck, which I'm told is fairly streamlined. How thick/thin a deck can one run?
60 is the minimum for constructed decks(decks that aren't built in a limited format such as a sealed deck or draft tournament). In sealed deck and draft events, the minimum deck size is 40 cards. You can have as many cards as you want in your deck though, as long as you're able to shuffle it without help. Eelektrik is right, generally you want to have the minimum number of cards in your deck, that way you increase the odds of drawing the best cards in your deck.
There's also another format which is generally quite casual called Commander(or EDH, short for Elder Dragon Highlander). In that format, you have one legendary creature which you put aside, and a 100 card deck in which no two cards are the same. There's a whole set of rules which you can find here:
http://dragonhighlander.net/rules.php
It's especially good for casual multiplayer games with friends. I recommend you check it out if you're into multiplayer with friends.