When I first started it was several times a day now it's once in the morning and once before I turn off the computer.
Once a day at most... Sometimes just once a week... And it's usually just too depressing, so why bother?
I check a few times a day, hoping to be surprised by new clicks each time I check, usually finding none. It's my main source of blog income at the moment. I've got a few affiliate programs running, had a few clicks but no sales, therefore, no earnings. I do about $3/day on adsense, with my highest day being just shy of $20. I get $3 for some clicks, $0.20 for others. I'm in the education niche, which I fully expect to be a low-paying niche, so I'm not totally dissatisfied with my earnings. I'm hoping to bump my average to $10/day to wipe out my student loan payments each month, and I'll be a happy man.
I'll check it every time I start getting slow and losing motivation. The longer I wait between checking it, the more motivation I get. Checking it helps remind me why I am doing all this work!
I try to actually limit the amount of times I check it. I have heard before of the superstition that the more the look at your adsense account, the less you earn because Google will think that the clicks are fake, and you are frequently checking up on them. I try to limit the amount I look at my account to about once a week .
I use the Adsense Notifier for Firefox actually, it shows up in the right bottom corner of your browser window. Its so good to see page impressions - no. of clicks - earnings anytime
Right now since my blog is new I am checking a few times a day. Once I know my ad positions are working I will probably check a bit less. Maybe once every day or so.
a few times a day. it's getting less as the novelty is wearing off. But on days when my earnings are great I tend to check more often to see if I'm going to break a record.