Longest for me was 3 months when I was working on the isle of sark.
I have to say when I'm not around it I never miss it and only when it's avaliable do I keep spending time on it.
That said I honestly only use it for 3 web sites and email.
This one, ebay..obviously... and a newspaper online when I'm away from the u.k.. apart from those I would rely on txts if I had no internet for communication.