I just updated iOS to 4.2. Ever after that, i got connection issue when browsing on the Internet. It is very frustrated to go back to settings to reset the wi-fi every few minutes. Anyone has a quick fix?

Check the Apple forums, their are 25+ pages on this topic, some of the cures suggested work for some not for others. The only real cure is to downgrade back to iOS3.2.1 until apple fixes this problem. Just keep in mind that many people have no problems at all, but a lot do.