Like many others here I always print to PDF - in fact until I read this thread it never occurred to me that people would check in online WITHOUT printing to PDF. Having a PDF not only means that you can print the hard copy at some other time, but also gives you backup in case you lose the hard copy and then find you need it to retro-claim miles.
Things obviously vary from country to country and from hotel to hotel, but here in Europe I have generally found that if I go to the reception desk with my USB stick they will be more than happy to print the file for me, free of charge.
On those occasions when I've not been able to print the BP I will just go to the airport without it. If I'm checking baggage they will print it at the bag drop - this has never been a problem. If I'm not checking baggage I will print it at the kiosk. With KLM (my usual carrier) this is now no longer a problem. It was in the early days, but now the message will just come up "You are already checked, select 'OK' to print your boarding pass".