I heard that if you use port 443 (the port usually used for https) for ssh, the encrypted packets look the same to your isp.
Could this be a way to avoid traffic shaping/throttling?
I'm not sure it's true that any given ssh packet "looks" the same as any given https packet.
However, over their lifetime they don't behave the same way. The session set up and tear down don't look alike (SSH offer a plain text banner during initial connect, for one thing). Also, typically wouldn't an https session be short lived? Connect, get your data, disconnect, whereas ssh would connect and persist for long periods of time? I think perhaps using 443 instead of 22 might get past naive filters, but I don't think it would fool someone specifically looking for active attempts to bypass their filters.
Is throttling ssh a common occurrence? I've experienced people blocking it, but I don't think I've experienced throttling. Heck, I usually use ssh tunnels to bypass other blocks since people don't usually care about it.