after 11 years of happy cross-cultural marriage, more positive comments below 
tough question. nothing comes to mind readily except silly superstitions, but i can’t think of any that were annoying or adhered to enough to be a real problem. i’ve been blessed that my wife’s family while very traditional taiwanese is also very big-hearted and straightforward, i haven’t experienced many of the in-law difficulties mentioned above. the initial meetings weren’t a cup of tea–their main concerns were their daughter being swept away overseas not to be seen again and the high rate of divorce in crosscultural marriages. we got over this pretty quickly. it helped that my wife while very traditional in many ways has never been the type to listen to whatever mom and dad say. i tried learning some taiwanese asap (they don’t speak any mandarin) and this helped a lot. i can also now bullshit in taiwanese with taxi drivers, a nice side-benefit 
[quote][ul][li]What are the biggest cultural differences you found in your marriage? [/li]
[li]What are the hardest things to accept or get used to?[/li]
[li]What were you not prepared to sacrifice when you got married? [/li]
[li]What are the biggest compromises you have had to make? [/li]
[li]What things has your spouse compromised on / failed to compromise on?[/li][/ul][/quote]
many minor things but nothing that couldn’t be worked out without some communication, which i agree is very important. language difficulties can be a big stumbling block here. fortunately this was never a big problem for us. there has to be some acceptance and give and take on both sides. you have to be able to give on things that have some sense behind them and are not intolerable while not bending on things that are really unacceptable to you and will always be a thorn in your side. understanding the local culture and the motivation behind seeming nonsense will really help too.
[quote]Which language do you use for normal, daily communication?
And then which language do you use when arguments/fights erupt?[/quote]
Mandarin, mandarin–sometimes a well chosen sentence of english 
a lot
without thinking for half a second
one i asked was “will you go back to the states with me?” i got a yes–with a condition of staying in Taiwan at least 2 years–but it took some long thinking on my wife’s part. that was 11 years ago, now she always bugs me to move back
we take the kids back every year, that’s about the minimum i could do and stay sane, that’s a rough one bq about the grandfather.
[quote]What single best piece of advice can you give to:
(a) the foreign partner contemplating a mixed marriage, and
(b) the Taiwanese partner contemplating a mixed marriage[/quote]
in any marriage trust is everything, keep it. for the cross-cultural bit hey give a bit, too much “our way is right” will have negative consequences down the road, of course your partner will have to give too.