As a less frequent flyer I'm not sure this will help but I guess you'd want all angles.
How much do you fly, in terms of hours, on a monthly basis?
2 hours (average 1 UK internal same-day return trip a month, used to be 4 when I worked for someone else)
How long is your typical layover, if you're not based in a hub city?
N/A (the UK just isn't big enough)
Have you ever left (or ever considered leaving) the airport during a long layover?
(long layovers have always been leisure, planned to allow an overnight stay en-route to a far-flung destination) I'd have to have quite a few hours (6+) before considering leaving an airport unless I knew the area well.
How often does business bring you near an airport, but not into the city the airport serves?
About 3 times a year, usually due to exhibitions that are being held near Birmingham, UK. London exhibitions usually entail going into the city.
How often do you use online airport services, such as mobile flight status notification, web checkin, etc?
Not a frequent enough flyer now, I've never had check in problems as I tend to arrive too early anyway although the KLM check-in at Amsterdam Schipol was handy (automated - just scan your passport and you're done - no queues).