Normally, matchmaking is done on a game by game basis. If you play well in this game, you get matches with more competent players in the next, and if you cheat you might get penalised in matchmaking pools in future games. Interestingly, Counter-Strike: Global Offensive is now taking into account more than just your CS:GO gameplay stats when matching you up with other players.
As part of a new system called The Trust Factor, users will be matched up not just based on their time with CS:GO, but also their overall Steam playtime and other stats in an attempt to match them with the players they would most likely get along with. In other words, it's not just putting together players based on skill, but on whether they tend to get reported or abandon matches or whatever other behaviour Valve considers undesirable.
The intention for the system is for players to issue fewer reports saying that they're unhappy with their matchmaking, or online play experience.
Valve have not explicitly outlined a full list of the factors that make up the new matchmaking system, but if you don't fancy it, there will still be an option to use the previous Prime matchmaking system which required users to add a verified phone number before playing.
Due to the secrecy around the system, at least a few players are now nervous their bad behaviour in other Steam games may impact their CS:GO experience. Only time will tell.