I have been having issues with this phone since I got it. I pretty much have to reboot it every day. It's not just my phone either, my wife has the exact same phone and she experiences the same problems as me. I used my old iphone and did a speed test on wifi and was downloading @ like 15mbps......then proceeded to try with the nexus s and it had like 58kbps download speeds. Also, I got sick of the data freezing up when switching from 4g to 3g, so I ended up turning 4g off......It's not that fast anyways. My iphone had faster speeds on 3g than the nexus s has ever had on 4g. Even with the latest phone update push, it hasn't changed. I am kind of regretting switching from my iphone due to the data performance issues. Oh well, I'm locked in on my contract so I guess I'm stuck with this buggy Nexus S phone for now. I don't even use the phone at home, I use my iphone and GrooveIP through google voice. It is extremely reliable in comparison. When is Sprint going to get off of the wimax frequencies anyways? The higher frequencies don't penetrate structures very well=poor 4G coverage. I wish I would have looked into that before making the switch from AT&T.
my first question is what is your Wifi Access Point set to on the router? Is it set to transmit wifi B/G/N frequencies? If it is set to N, what channels are you using and are the in the 2.4Ghz band or the 5Ghz band?
The Nexus S 4G will support Wireless B/G/N but only in the 2.4 Ghz range. By default the Nexus will attempt to connect with Wifi N if "mixed mode" is enabled on a B/G/N capable router.
That should give you a starting point.
This will probably be deleted, but one of the reasons you're having such terrible wifi signal is because the NS4G has antenna issues.
3g/4g/wifi and bluetooth signals all are attenuated compared to other similar devices.
Samsung and Google are both aware of the issue, but it's likely hardware, so the attempted software fixes didn't improve things much.