MBK is more than shopping
My girlfriend and I did do some shopping at MBK -- a 1 gigabyte SD card for my camera (700 baht or $19), a good quality tee-shirt (195 baht or $5.40), tiny sweets formed into colorful copies of vegetables, Paul Mitchell shampoo and conditioner, etc.
But even more interesting for us was the food court on the 6th floor which has around 20 counters, each with a different kind of food. We ate lunch there 3 times. My friend tended to eat chicken, while I went to counter C-8, which had only vegetarian food. For the 2 of us lunch came to 100-180 baht ($2.75-5.00). You pay with prepurchased coupons. Be sure to get a refund for unused coupons before leaving the store.