I also believe there is a 2 coupon / 2 discount limit. Calling them in will not resolve your issue because Dell's customer service may not take the coupons into account. This is what happened to me a few weeks back. I saved an item to my shopping cart and was going to place the order the next day. Well, when I checked back into my cart, the item's price had jumped $70. I contacted their customer support number and they sold the item to me for the previous price, but would not allow me to use the $25 off coupon - plus, I lost out on using EBates. However, they did give me free overnight shipping and on my next two orders, the shipping will be free if I go through one of the agents that gave me his number.
Getting back on topic. If you're trying to stack a $25 off coupon and the $30 off coupon, they won't work together. However, If you're trying to use the 10% discount for cameras for this weekend along with one of the $100 off coupons, you should be able to use the two together. PM me if you have any additional questions.