Haha, I actually cleaned our tub yesterday :D It needed it badly, mostly because it was a little green from me dyeing the hair in my neck area green a few days ago.
Don't remember when we last did it before that though
It's always so much work, I hate hanging upside down scrubbing it.
I don't use very aggressive cleaning chemicals though, we have this mineral-based stuff that's just really effective at mechanically scrubbing basically any kind of surface. So no horrible fumes, luckily, otherwise I'd probably do it even less, I hate these smells so much.