Full disclosure: I like "stuff." I have liked "stuff" since I was a wee elf. I get great pleasure from having tangible mementos from my experiences (I do not, however, get great pleasure from trying to find room for the "stuff," but I am always happy when I see the "stuff," so it's worth it :).)
So people often ask, "do you save your Playbills?;" "why?" "what in the world do you do with them?" and/or "do you ever look at them again?" As already confessed, I tend to be a "keeper" and "chronicler" type anyway, but honestly I think I'd encourage even the collection-averse theater-goers to think twice before throwing away these wonderful (and included free with your ticket :)) mementos. The Playbill for each show is actually an issue of a monthly magazine that contains a full record of the show you're seeing (and contains Broadway news for that month about other shows and happenings). It will also sometimes give you a history of that particular theater (in a feature called "At This Theater"); and perhaps help jog your memory later when you want to brag to your friends that you saw a now-famous, but previously lesser-known actor in the show. For me, this would be the original cast of "Rent" that included Idina Menzel, or Debbie Allen in "Sweet Charity" or Karen Dotrice (the original "Jane" from the movie "Mary Poppins") in "Othello," just to name a few.
At the risk of sounding like I'm being paid to hype Playbill (I'm not at all; I pay them for their stuff, not the other way around :)), Playbill.com has an online store that sells show and Playbill-branded merchandise, and my favorite exclusive item from them is the Playbill binder in which you can store those Playbills (and tickets, if you want) in plastic sleeves. Especially if you go to the stage door and get your Playbill signed (and you should :); go here to find out why!), you'll enjoy going back later and remembering the fun you had meeting the actors. I have filled several of these binders already, and can whole-heartedly recommend them. They also sell frames specially made to hold Playbills (and tickets); a good option if you have one that's extra-special, and was signed by that actor you love or even the entire cast.
I have been particularly grateful this season that I saved my memorabilia from the original production of "Godspell" at Ford's Theater from 1972-3. "Godspell" was the show that really flipped the switch for me and made me the live theater mega-fan I am today. I loved so much being able to share these mementos with my niece, who is now almost the same age as I was when I first saw "Godspell," and then take her to see the revival and make new memories with her.
However, even if you just toss your Playbills in an old shoebox, or up on a shelf for a while, you might find that you get a kick out of pulling them out and reminiscing, with a bit of help in filling in the gaps in your memory :). Collecting/saving is not for everyone; but it sure works for me!