There is a fairly extensive support thread over at Google — that stretches from January of this year all the way to the present — that details issues some Nexus One owners are having with Wi-Fi connections. The bug reports all read like this: your N1 connects to a wireless network; you put the phone down and the display eventually goes to sleep; while the screen is off the N1 is still technically connected to the wireless router but no data is passing through the device; the device sees itself as having a connection to Wi-Fi so it does not revert to cellular data; no email, Facebook, Twitter, etc. updating/data is flowing in the background. The thread reports that the only way to remedy this issue is to flick Wi-Fi off then on every time you turn the screen on, or to turn Wi-Fi off completely. The thread reports that the glitch happens primarily on AT&T model Nexus Ones and later models of the T-Mobile N1s. The group of affected users have seemingly flushed out the Google suggestion that it is a specific type of router causing the issue, and no specific Android firmware can be pegged as the culprit. We want to hear from you AT&T and T-Mobile Sexy Nexy owners. Are you seeing this issue?
UPDATE: Apparently an update to remedy this issue has been pushed into the AOSP repository, have a look for yourself. Thanks to Howard for passing this along.