I have Haiku as sole OS on a Thinkpad, not my primary machine but some days I'll work the whole day on it no problem - it's a really enjoyable experience in fact.
So if I had all that, I could use Haiku as my home/hobby tinkering machine. I would still need a Mac, Linux or Windows machine to do some other heavy lifting, but I already have three computers at home, so no problem.
It had working Google Calendar sync at one point, dunno if it still is. It could definitely use some work, though.