I have this problem as well. I was able to play for the first few days after purchase (Steam) with no problem. However I have started to get "Connection to server has been lost." very frequently. It's extremely frustrating especially when the only good ping server is a Battle one.
Anyhow, I use a cheap **** USB wireless adapter to connect to a router. I have my share of issues with connectivity, but at the time of M&B disconnects, it seems fine. I also get 999 ping for about 20 seconds when playing Battlefield: Bad Company 2, after which the game runs fine, no disconnect at least.
I have updated the firmware for my router, added some M&B ports to the list (unsure if it did anything), updated BIOS (had problems with USB connectivity), but still very problematic online gameplay.