First, I like to fold the magazine pages that I want to keep. Then, I go back later and tear them out. While watching TV, I cut out (quickly, not neatly) the layouts and ideas that I like and adhere them in a binder of ideas. I just put them on binder paper in different categories. The categories I use are cards, layouts and projects. Within the cards section, I break it down into thank you cards, birthday cards, and holidays. In the layout section, I break it down by layouts I like in general, and the ones that I liked because of a specific technique. I actually go back and label the techniques for those, so I remember. Then, I save any pages that refer to a contest or website that I want to check out and keep those pages by my desk until I'm done with them.
After all that, I don't mind throwing away the magazine because I have pretty much scoured it for all that I wanted!
It sounds complicated, but it's the perfect thing for me to do in front of the TV after dinner and it doesn't really take that long, once you have the system going. I just keep scissors, adhesive, the idea binder, and the magazines together in a tote bag.
Hope this helps!