It'll depend on what you write, who you get at the border, and what else you do.
For example, I've seen a person not have a hotel when they arrived at US Customs. He literally turned and asked anyone behind in the queue if they know the address of a hotel, and someone named the one from Pretty Woman on Rodeo Drive. So he wrote that in, and handed it to the border guard, who shrugged, stamped, and completed the process.
Now for a lot of countries, having that address down is rarely used. It's handy in case of emergency if they needed to contact you (assuming you've not moved on).
You may not intend to lie. You might put down a hostel, get there, find they've lost your booking and are full, and you have to stay elsewhere. You may even intend to go to town X, your car breaks down and you have to stay in some roadside inn. Things do change.
However, it's an official government form from a foreign country. You NEVER want to intentionally lie on these. So if you do know the address, it's best to put it down. And put down the truth. I once spent 30 min in Orlando International Airport while the immigration officer pulled up the website of the place I said I was staying at, and checked the flight that I said my friend was coming in on, and confirmed the address and whether it was even possible to get there that night.
So to answer your question, yes, they can and do check. If they can pull up the website, there's nothing stopping them calling the hotel to confirm your 'booking', especially if you don't have paper evidence of said booking.
Side note, I suppose you could try saying "I'm staying with my friend, and meeting him outside, so don't know his address" or something similar, if you really didn't want your friend's address on this, but then they might want to call the friend, and if your stories don't match....more problems.
Bottom line: honesty is the best policy here.