How long can stay in USA

- 30 day, 90 days aand 180 days - all these 3 are standard for travelling visa. It depends on the Custom officer which one he likes to give you. The date will show on the card that you received when you enter the USA.

- I have heard lots of people saying even you are allowed to stay 180 days in the United States, but it is better not to stay that long in USA. You should return to your country within 2 to 3 months. This will help you in getting an USA VISA next time. (This is not from any official information, but I have heard someone saying this before. )

- In case, the days that US custom gave you is not enough. You can apply to extend the allowance of your staying as a traveller. You can find out more information about how to extend from http://www.uscis.gov

This really depends on the immigration officer. There are no specific standard as to how long they allow you to stay in US. Therefore, your friend can upto 180 days..In fact, the immigration officer will put a date stamp on your passport showing you exactly which date is the last day you can stay in US.

for your friend who got 180 days limit..is it on a tourist visa or work visa.
normally, tourists allow upto 90 days of stay in the US. like i said before..it really depends.