My DH has had one for about 7 or 8 years now and I can't sleep without it, LOL!
It didn't take me anytime to get used to it, it was such an improvement over his awful snoring! Seriously though, it made such a big difference for both of us, he was so loud that it was keeping both of us up all night. Once he got the Cpap machine we both started sleeping through the night. His newer machine is very quiet compared to the old one, it is just like a fan set on low, maybe not even that loud. It took more time for him to get used to it than for me, even now some nights he will forget about it and try to sleep on his stomach and will dislodge it and I have to hit him to turn over and put it back on. HTH!