durrettd is dead on with his temperature statement.
I've done blind tastings for my friends. I've poured the exact same beer into two different glasses (one frosted and one room temperature). They almost always like the flavor of the room temperature glass better.
There is a reason for this. When temperatures are below 55F, the human taste buds have difficulty tasting maltiness. When a malty beer is made well and is balanced, it will taste best at 55F or higher. If you put it in a frosted glass, as you drink, the liquid is thinner at the top, and as the glass is tilted to take a sip and it takes the beer temperature down too much for your taste buds to have the ability to detect the full range of flavors. Once the beer has sat in the glass for a while (even a frosted one), it will eventually warm up enough to allow you to taste the full range of flavors and the beer comes into balance, at least as far as your taste buds are concerned.
This begs the question, why do commercial mass brewed beers (Bud, Bud Light, Millers, Coors, etc) taste better ice cold? Then answer is that there is very little malt or hop flavors to get out of balance, so the flavor is dead on, no matter how warm or cold they are. Thus, ice cold is better with those beers, because ice cold is great.
If you want to be able to enjoy your porter ice cold, you can brew it extremely malty, and it will taste best at ice cold temperatures. However, as it warms up in the glass, it will not taste as good as it did when it was ice cold.