They make a lovely house plant in their own right, but the fact that they produce large numbers of such wonderful little fruits makes them a wonderful option for anyone in a Northern climate trying to eat locally produced food.
I was given a gift certificate for one of my favorite garden shops for my birthday, and a Meyer lemon tree was on the top of my list. Fortunately, they had one left when I got there last weekend, so I quickly snapped it right up. It's a more mature tree, which means it wasn't exactly cheap, but it's got half a dozen full sized fruits on it, with lots of little ones on the way, so it was well worth it. I plan to keep it in the dining room near our south facing patio doors during cool weather, moving it outside in the warmer months.
I think I see a Key Lime in my future. Who says you can't grow citrus fruit in Canada?