Reasonably so. I had to bolt down my gazebo and attach sandbags to the legs because it'd have blown away, metal frame and all, if I didn't.

Note that a couple of decent sized hooks bolted to the wall can hold a lot compared to trying to weight something down to the ground without firmly attaching it. If you need to attach it to a pole or a post, then you probably want to make sure that side is weighed down quite a bit.

The wind is also the main reason why I have the carabiner hooks so that it's reasonably easy to unhook and fold it up when it gets extra windy without having to try to untie ropes etc..