evblazer

I do a quick feel before I get on the bike when leaving home/work/store/rest stop on a ride/...
On both my 25 and 28mm tires (both 110psi) I end up pumping them up every day that I'm riding them. On my current 32s (85psi) I can usually got a few rides without much of a problem.

I don't use some lightweight race tubes or tires either

ItsJustMe

I check daily by sitting on the bike and looking to see how far down they're squishing. I only bother checking every 2 to 4 weeks. In 4 weeks they usually have leaked down from 80 to 50 PSI. I probably should check them every 2 weeks.

FredOak

I found that if I store my bike in the garage and it's hot out I lose air, so I'll inflate them each morning. In cooler weather I'll give them a push and if they seem OK, I'll do them on the next ride.

hankbrandenburg

I add air to my tires every morning before I leave the house to bring them up to 100 PSI. I am a 250 lb clyde and I seem to pound about 20 PSI out of my rear tire and 10 PSI out of my front tire during my 36 miles of riding each day.

rajman

About once every week to two weeks... Whenever they feel squishier. Usually this means that the pressure has dropped at least 20-40%

elTwitcho

Every other day. They're 120PSI 23c tires and I ride a few hours per day so I lose pressure quick.

tsl

Daily, before leaving the house.

Scorer75

Every day.

cyclewolf

Daily.

lil brown bat

I check not less than once a week and top 'em up as needed.

Bionicycle

Before the first ride, every day I ride.

Pig_Chaser

Used to be daily, then it fell to bi-weekly, and now i'm at weekly. I'm finding that my 120psi 23Cs only loose about 20psi max over the course of a full 7 days - and that's in the rear... less still in the front.

Catgrrl70

Ditto.

CACycling

Sunday night my commuter gets filled to 105 psi and loses about 10 lbs. during the week which is acceptable to me.

Wife's grocery getter gets filled to 100 psi whenever she remembers to do it. (Since she keeps it at her mom's, it isn't my job anymore).

Road bikes (mine and wife's) get filled to 120 before every ride.

The 4 MTBs get topped off to 60 psi every couple of weeks whether ridden or not.

CommuterRun

At the beginning of the week, or when I switch to another bike.

striegel 

When I rode on 27 inch tubular tires, I pumped them up every day that I rode. The pressure I liked was at 120 psi. The extremely thin rubber inner tubes would typically lose 10 psi by the next day.

The 20 inch x 1.50 inch tires on my current folding bike take 85 psi and I re-fill them on Sundays before I go to bed at night. I might find that after a week, the pressure drops by a bit less than 10 psi.

making

Until a few weeks ago I pumped them up every night. I bought a pump for my office and now I only pump them up every few days. I guess I dont get so worried about it because I can pump it up at work too. Pinch test.

Hydrated

Every morning. I do everything humanly possible to avoid a flat on the road. Another benefit is that it ensures that my tires are at their optimum rolling resistance.

taliesin

At least every other day (Read: daily, except for when I forget).

BA Commuter

Once a week. I also check for any loose spokes and/nuts. Then, I'm ready to go for the next week!

abbynemmy

I check and fill mine every morning.

Tabor

Every morning. I hate pinch flats.

Caribou2001

I do the squeeze-test before every ride (also check brakes, and do the drop-test for rattles, and finally check for signs of intentional or unintentional "modifications" {from bikes parked in the same space or from curious onlookers}). I'll also pump every few days or before a longer ride. (Presta 700x32's)

stringbreaker

I would check to see if the tubes have a bad valve stem. they shouldn't need to be pumped up that often or at least none of my bikes do. Once a week is good but I do the squeeze test every morning.

devianb

I squeeze my tires every few days to check for hardness, but I only need to re inflate a tad each month.