I remember reading on here that if you are one of the customers with "up to 8Mb" you'll need to check the "connection settings" part of the plus net member centre.
Check for "Broardband Interleaving" if it's on they have increased the latency of your connection for higher stable max speed. If you're a gamer this isn't actually a good thing. You should have the option of turning it off but this means you might have to boot your modem / router and settle for a lower max speed.
Also, there are 3 ports you need to open up if you are using a router. Can't remember them off hand but if you google it I'm sure they will come up. Opening these ports has solved ALL my connection issues with Live!