It's fairly uncommon, especially if you don't have ram air or ducted air, where the under-hood heat warms it enough first. I've only had it twice in Florida with the high humidity, and both around 45 to 55 degrees. It's something that may happen and folks have no idea that's the issue. I didn't the first time, and pulled the air cleaner top to check for a stuck choke or something (it felt like lugging the engine in high gear gear), and found the prettiest white 'snowdrifts' in the primary throttle bores about 1/2" thick. Once you shut the engine down, it melts in seconds to maybe a couple minutes. The second time, I sat at the intersection with the engine at fast idle until I saw someone I knew. I flagged them down just so I could show someone as proof I wasn't BSing at the next club meeting. LOL
Personally, I don't worry about the possibility of carb icing, and I block the intake manifold exhaust crossovers along with a thermal spacer to limit carb overheating. I don't see much really cold or freezing weather with my cars. Others may need more heat.
BTW - I don't know when they stopped with the coolant spacers, but my '78 460 had one stock.
David
[EDIT] PS: It's possible alcohol in our gasoline may aggravate the issue. Hmmm...