I haven't noticed such disconnections myself. Could it be some local (e.g. ADSL modem/router) configuration? Did things work OK before and did these disconnection problems only crop up later? Did anything change between when it worked fine and started exhibiting problems?
I'm having similar problems with my Esat BT Zyxel router. Every time I plug everything (PC and router) out, I have to manually reset the router (rest button at back) and log back on through the router's control panel.
Is leaving everything plugged in the answer?