Frost Death Knights are incredibly powerful in Cataclysm.
OUT OF DATE (Look for updated guides soon!)
Despite the fact that as of 4.3 I no longer play Frost with my Death Knight, I still have an incredible amount of respect for it. It is without a doubt the highest AoE DPS of any Death Knight spec, and in many cases (depending upon fight mechanics) it is the highest single-target DPS Death Knight spec as well. The primary reasons for this are twofold.
1) Frost has Howling Blast. This is a huge cleave, and with large amounts of mastery it hits your enemies like a freight train. It also will apply one of your two diseases very quickly. Additionally, Howling Blast can be a cast without any resource cost due to the passive Rime proc.
2) All of Frost's primary stats scale quite well/properly. While this particular point isn't immediately apparent, It will be emphasized in my later "Unholy DPS" Post.
In addition to doing immense amounts of damage in any situation, Frost also has the additional advantage of having excellent raid utility. Frost can interrupt casts every ten seconds for free (if specced into it), Frost can also (like every other Death Knight spec) apply some wonderful debuffs to debilitate any enemies with its diseases, and can also spec into Chillblains to slow huge hordes of enemies effectively. In fact, before all the nerfs to Dragon Soul, Chillblains was one of the most recommended ways to successfully get though Heroic Spine of Deathwing.
Check out the links below to get more specific (and better :P ) information on Frost Death Knights.
A great, simple, straightforward guide that assumes nothing about the player's level of experience. An excellent way to get started!
A very nice (although outdated) guide that assumes you know very little, while managing to be helpful for players of any level of expertise.
As always, Elitist Jerks is THE go to resource for deep and well researched class/spec information
Thanks for reading, and as always comments of all varieties are welcome! Don't be shy!