LNB drift is really frequency drift (the LNBs are tuned to a certain frequency). The newer receivers can compensate for some amount of drift, but if it gets too high you will lose signal. Many times LNB drift is affected by temperature. A few years ago I had an LNB that drifted with temperature. During the day, as the temperature increased, the LNB drift got worse and I would lose channels. Later, at night when it cooled off, the drift would decrease and the channels would come back on.
Back then, Dish would replace the LNB if the drift was 8 or more. I don't know what their policy is now, but you should call them. They will most likely replace it. If you don't do anything the drift will likely get worse and you will lose channels.