My experiences:

UA: Plastic (w/o mag stripe), no flights required
DL: Plastic (w/ mag stripe), 1 flight required (4-6 week wait as is typical)
AA: Flimsy plastic (w/o mag stripe), mileage activity required (not necessarily a flight--mine are all from cereal coupons)

I have FF accounts also with US Air, Southwest, Northwest, and Continental (most with little or no active miles). These all just do the temporary paper cards and require a flight before issuing a "real" card.

As for hotels:

Marriott: Plastic card (w/o mag stripe), no stay required
Hilton HHonors: Plastic card (w/o mag stripe), no stay required
Six Continents: Plastic card (w/ mag stripe), no stay required
Radisson: Plastic card (w/ mag stripe), no stay required

Wyndham does require a stay, but as they STILL haven't sent my card (for an April '04 stay) and have even deactivated my account online, I can't say what their card is like. My SPG card is "in the mail" and didn't require a stay. Not sure about Choice Hotels as I've never stayed there and only recently signed up for their program.