It's tolerable, but it's hardly a stellar experience. Things like suspend/hibernate, fan control, etc. are problematic, even though they're fine on most other pieces of hardware on the market.

I always sigh a bit when I hear people recommending installing Linux on a Macbook, because they're not getting the full experience - they end up thinking that Linux is buggy and doesn't support these functionalities well, when the truth is that it does, as long as you use hardware that is actually supported.

There are a number of reasons that Apple hardware will probably always be a sub-optimal platform for Linux. There was a HN comment a while back from one of the Linux kernel developers responsible for maintaining the MPB drivers who explained why this is the case, though I can't find it.