After so much monitoring I have came to the conlcusion that it's a signal issue. I run a digital agency and have been using mac since 1984, I know them inside out. I am also the guine pig in the agency trying out first new things and have my own tech team working out solutions.
Boils down to:
The problem obvisouly is Mountain Lion and how it react to the signal of the Wi-fi.
Ethernet always works and most of the time I am on ethernet.
Using a USB dongle works well
Sometimes it connectes to wi-fi sometimes it doesn't. If I try to wi-fi first in my lounge (3mt from router) it does't work, then I walk to my bedroom and it connects, then go back to the lounge and it works and stays connected but then sometimes it drops out. There is really no explanation or reason I think it's how ML interprets the signal from the wi-fi.
The trick of renewing the DHCP doesnt always work, sometimes it does. If you delete the whole WI-WFi and re-create it sometimes it fixes it sometimes it doesnt. Again it's a bit of a russian roulette. But from my bedroom (6mt from rotuer + wall) it never drops out and always connects.
I found ways to position my mac so it works, so it's not an issue as much although Apple needs to fix it, so I am checking everyday when 1.8.1 is ready.
So I hope I am being helpful.
Mac is: MacBook Pro, 2.2 i7, 16GB Ram, 1TB Hardrive.
Mountain Lion was an upgrade although I normally would just do a clean install.
PR - Another issue I have with ML is that the Empty trash is Very Very and I mean Very slow. But this is another issue. All in all ML purrs quite well and better than Lion.