I understand that there may be a requirement to be in Switzerland for 180 days per year to maintain residency and work permit. Does anyone have any details on this? How is it monitored, tracking, regulated? Does it affect flights to USA, border crossing in Europe, travel for work, etc?
I have heard that there is an agreement with Germany about this - if you are outside of Germany for more than 182 days per year, you are then liable for taxes in the country where you reside (in this case, Switzerland) instead of Germany. For proof, you would need to show a rental contract for a Swiss apartment or have hotel bills to prove your claims.
I was discussing this with a friend in Germany recently - her husband is a trucker in Switzerland. He drives to work on Monday morning, picks up his truck and spends 5 days on the road, usually returning home Friday night or Saturday morning. He can claim the 182 day rule and has his "Fahrtenschreiber" (tachograph) and his log book as proof that he was in Switzerland (sleeping in the cab of his truck) over 200 days per year.
My understanding from our HR department is that you need to be in Switzerland at least 6 months per year in order to maintain your Swiss work/resident's status as a non-EU 'B' permit holder. Monitoring this would be a challenge for Swiss authorities, I suspect, due to the potential for plenty of unmonitored travel within Europe. Of course, they know when you have left Europe.
The only implication this has for your US tax liability is if you spend time on business in the US or have not established foreign residency yet for tax purposes (tax home). In all cases, US citizens are liable for US income taxes, but if your tax home is still the US or if you have business trips in the US (interpreted as making money in the US for tax reasons, even if your employer is not in the US), your liability is higher.
Truth in advertising, this is experiential/anecdotal, not professional, information and should be treated as such.