Prevent overheating when tethering When I tether my phone and download big files or large numbers of them, and download is non-stop for a few hours, my phone (Nexus One) overheats. Is there any way to prevent that, except avoiding overusing the net?

This has happened in multiple devices, so it's not a hardware malfunction; it also happens both in the original ROM and CM7.
You could physical approaches, such as setting a fan blowing across the phone or other airflow maximization (e.g., if you can stand it up, then both the back and front are exposed to air).

Lastly, if it doesn't interfere with the radios, you could try resting it on an upside-down heavy-duty aluminum jellyroll pan ("cookie sheet") which will function as a heat sink.

You can combine approaches of course; a fan blowing over the jellyroll pan will be even better.

That you're getting several hours before overheat tells me you're close, so you probably won't need to do much to dissipate the heat. Standing the phone up may be enough. A fan almost certainly will be.