Yes, I have.
I had to give up my basset hound, Pork Chop when I moved into my apartment ages ago. I couldn't afford the pet deposit, so my parents took him. I never took him back, though, after I could, because he was so happy with my parents, and I know that they love him and care for him just as much as I do. He's such a handsome grown man, now!
I've also had to give up my guinea pigs, Archie and Jughead.
I adopted those boys off of craigslist. I frikken loved them. They were my piggie boys! A few months after I got them, I started sneezing. I figured it was the hay, so I found ways to get around smelling it so much. That helped, but then the bumps started.
I noticed when I had the boys lying on my chest or arms or legs, I'd break out in tiny hives. I was allergic to their fur. I was SO devastated. when I came to this conclusion. There wasn't a way around it...
So, when I met my girlfriend, I researched piggie rescues in my area. None in my area could accept anymore animals, so I found on between my city and my girlfriend's city. When she came up to visit me before I moved, she packed the boys up and took them down there. I was so sad.
However, the boys got adopted within a week, and a few months ago I saw a picture of them with their new humans. Archie was SO happy. Apparently the four-year-old that they live with reads them a bedtime story every single night.