That depends. A $25 RainForest Café GC costs 3,250 points. Reading and clicking on the link in an email is usually worth 5 points. I get 2-3 emails per day.
Some trial offers and free sign up can be worth quite a few points. Right now, you can get 1,500 points for trying AOL. You can get another 2,000 points by applying for and using a MyPoints MasterCard for the first time. Referring friends can earn you up to 1,000 points per month.
So, yes you can get something without ever shopping thru their portal but online shopping is probably the most consistent way to earn points with them