Has anyone else noticed getting fewer bars in locations that you got a full signal before jailbreaking 4.2.1 with redsn0w 0.9.6rc8? Does the weather being really cold affect 3G signal at all?

Anyone?

For the avoidance of doubt there is nothing in the actual jailbreak which can possibly effect the 3G signal strength directly. Only apps which are specifically coded to mess with the radios could have the potential to do this, and even then its unlikely you would see a drop in sensitivity... I dont know of any apps which do this.
It is much more likely you are just winessing some type of environmental interference or combination of effects. Weather can be a factor, but not usually a visible sustained drop in bars...