Not a problem if your magazine is not loaded to full capacity. If you have a Ruger Mark II, for example, load it with 8-9 shots. Just not loading it to full capacity should give you plenty of wiggle room with modern magazines. If you're using an old Colt 1911, I'd swap magazines every few months. I had a friend who, as a child, was saved when one round went off in a 1911 that had been loaded for several years. The first round fired, but the second jammed. He had the gun pointed at his younger brother.
I wouldn't count on modern magazines weakening, however.
Finally, if you're using a cheap magazine, you can't count on it anyway, much less if it's been loaded for awhile.