IF we are to believe the Verizon leak which was correct about the first OTA update, it "should" be released on or slightly before Jan 22nd.
The only thing is, this was leaked almost 2.5 months ago and in software development a lot can change in that amount of time. While a lot of the 2.1 code is posted on the google source code repositories, there hasnt been (to my knowledge) an official 2.1 source release, only the SDK. This could mean any number of things.
- There could be patches being added to address any security holes found
- The 2.1 that is on the Nexus One "might" not be the final 2.1 and there could be an OTA update in the near future for it as well with the final 2.1
- Google could just be sitting there and taking their sweet time to release the official source for whatever reason
To make matters even more complicated, it could also not even matter as Motorola might have the final 2.1 code and might "hopefully" be adding Droid specific optimizations/driver updates, maybe updating some of the bundled apps, possibly updating the device firmware as part of the 2.1 update to fix any issues, etc.