I'm currently waiting on my MorphOS replacement machine to arrive in the mail, so I'm unable to test those sites for you ATM.
Your best bet is to subscribe and post this question to the MorphOS mail news feed/forum thing mentioned on their homepage, or subscribe and post this to MorphOS zone. They'll be completely honest and very helpful if not very convincing.

Anyhow, as I said I can't test those web pages or Google docs, but I do know that the OWB port on MorphOS is FREAKING AWESOME and is very YouTube friendly amonst other things. I don't really remember having any comparability issues between it and my various favorite web sites.
As for Office docs... No idea, I just use Final Writer and or AmiWriter as I'm not in school so I am not bound by Microsoft formats.
About any classic apps that don't call upon Paula or the ECS/AGA chips should work and work well!
Make sure you get a Mac with no less than 64Mb of RAM or else your multi-tasking will be limited as will your gaming experience, GFX apps experience, and so on.
There is a nice app that allows you to search for and download software for MorphOS, and of course you still have acess to a ton of software on Aminet!

Um... I'm on an iPod and can't type all this out, but seriously, MorphOS is GOOD under the hood and doesn't just rely on a few flashy games or what not for it's fame (no offence Aros I love you!!!)
It seriously does feel like the next evolution for Amiga OS. I had just as much fun exploring it as I did my original Amiga.