I'm also interested in monitoring temperature (and humidity) to determine at which temps and conditions my system works, but figured that it would be neat to also be able to log the temperature as a function of time throughout the duration of the entire trip. My Suunto vector watch used to do this, but after 12 of nearly continual daily use, my old Vector watch isn't doing so well... still works, but some of the buttons seem to get stuck.
I did some googling, and there is a product out there called iButtons, they are tiny "therocrons", mainly for logging temperature for scientific purposes, they seem very robust, waterproof, tiny and weigh about 3 grams!
The cheapest one I can find is: http://www.embeddeddatasystems.com/DS1920-F5--iButton-Thermometer_p_94.html but then you also need a USB or ethernet adapter: http://www.embeddeddatasystems.com/DS9490R--USB-to-1-Wire-iButton-Adapter_p_131.html
and there are many iButton models, depending on temperature range and sensitivity, and they also have ones that monitor humidity.
At about $35 after the dust settles, for a device with a non-rechargeable non-replaceable battery (though, it apparently lasts many years), just to log temperature for the trip is a bit steep. I think it'd be neat to know the temperature and humidity as a function of time on a trip though, especially for those interested in rigorous gear tests or review sites.
I'd love to find something cheaper, as I think it'd be neat to see the temperature continually over a trip.