However it is minor upgrade but still it will fix wifi connectivity issue, those who were using swype keyboard seems to have a problem with the keyboard after this update but this issue does not appear to be occurring for all the users. It is an worldwide update, so it will be pushed to all the nexus one users, still if you want to manually update your nexus one to 2.2.1 follow the procedure below.
1. Download the Android 2.2.1 firmware for the Nexus One from here
2. Rename the file update.zip and copy it to your microSD card via USB. [Note: make sure the file is named update.zip and not update.zip.zip.]
3. Power down your Nexus One
4. Hold down the “Volume Down” button as you power the phone back on.
5. A screen should appear showing your phone’s system searching for various files. Scroll down to “recovery” and press the “Power” button.
6. When you see the triangle with an exclamation point symbol, press the “Power” and “Volume Up” buttons at the same time.
7. From the menu that appears, select “Apply sdcard:update.zip.”
8. When the screen displays “Install from sdcard complete” select “reboot system now” and wait for the phone to power back up.
Please note: The 8th step will take a long time, so be patient – Enjoy android 2.2.1 on your nexus one once it power up again.