my guess is that logitech is still on their proprietary 2.4GHz goodness, which is all amazing, except 2.4GHz.
if the 2.4GHz band is completely stuffed in your area, it is stuffed for your mouse as well.
a very silly way to test this is to grab the antistatic bag of your motherboard (if you kept it) and put the receiver and mouse inside. if it works better, its the band thats stuffed.
now, if anyone claims to say you need a full seal on the bag for it to work.. yeah.. but putting my phone half way inside of an open bag is enough to completely cut all wireless connections, so i guess they're pretty effective agains 2.4GHz