Samsung Vibrant :: Intermittent Connection / Errors With WiFi

I have the same issue with 2 separate Vibrants, actually 3 Vibrants counting the one I took back.I have problems connecting to either the market or internet across multiple browsers while WiFi is on.With both phones, it seems this problem is intermittent and across different brands of routers at different locations.
An example is when I try to enter the market.I sometimes will get to the market home page but when I try to pull up my downloads it comes back with an error message saying connection failed.Once I turn off WiFi it works perfect in 3G, or if I leave WiFi on, go back to the home page and then try just a minute later it connects without a problem.To make matters even worse, the problem persists while using apps that connect to the internet such as The Weather Channel.The problem is very intermittent.Sometimes I have no problems connecting, while other times it won't connect at all until I turn WiFi off or even reboot the phone.Both phones behave the same way.I've gotten to the point now where I just leave WiFi turned off because it's so unreliable.I know it's not the WiFi signal strength either as it is just as likely to happen with the phone a few feet away from the router's antenna as it is when it's 50 feet away.