Make sure you have DSL chosen as your connection type in the MP Options, and try to join servers with the lowest ping possible.
A major connection backbone for the US broke down the other day, and Im not sure if it has been fixed yet. (From what I hear it is) THis may had a part in the issue as well.
If you want to tweak your connection (At your own will), visit
http://www.dslreports.com and you might want to also look into the program iSpeed.