First off: in the NEW ICC, all players are equal!
And no, there's nobody more equal than others.
We all, and I mean all, start with a 1500 rating in all rating categories.

Everyone starts at the SAME level, from the super-strong GM to the novice.

You'll compete in four different categories of rating:

• Bullet
• Blitz
• Rapid
• Classical
   

How to determine which category you're going to play in?

First, we need to understand what "etime" is.

etime is the initial time plus 2/3rd of the increment.

For example, a 2+12 game has an etime of 10 (2 + 2/3 of 12 = 2 + 8), while a 5+3 game has an etime of 7.
 

Now, let's see how we have defined the rating categories.

• Bullet: games with an etime less than 3;
• Blitz: games with an etime greater than or equal to 3 and less than 10;
• Rapid: games with an etime greater than or equal to 10 and less than 60;
• Classical: games with an etime greater than or equal to 60.

If you join one of the pools, your rating will be updated accordingly.

The new ICC is using the Glicko 2 rating system.

The system was developed by Mark Glickman in 1995 as an improvement on the Elo rating system and was initially intended for primary use as a chess rating system.
Glickman's principal contribution to measurement is "rating reliability," called RD, for rating deviation.
In the Glicko 2 system, Glickman introduced a new variable to calculate rating changes after a game: volatility. The RD is what drives the formulae to calculate the rating changes after a game. A new player starts with a high RD (350), which decreases progressively when the player plays more games.
But, and here is the main difference with the ELO system, the RD grows again when the player is inactive for a given amount of time.
Therefore, we can say that a player has a "provisional" rating when he starts and for a given number of games (20 games, depending on their opponent's rating status); that means that he's expected to gain or lose a lot of rating points after a game. But if the player doesn't play any game for some time, his status changes again from "established" to "provisional."
Glickman founds his reasoning on the reliability of a player's rating, and that's the most important improvement over the ELO system.

If you are interested in the mathematics of the algorithm, HERE is a link to a PDF file.

You can also read the article on Wikipedia.