I've always been tempted by a trailer, but the main thing that's put me off is the resistance of the extra wheel. I do have a trailer, but it's one of those kid's ones with two wheels. I've used it sometimes to transport stuff other than kids, and have found that the resistance is a pain, but then again, it's a heavy trailer with two wheels and one of those sprung attachers, so I don;t feel it's fair to compare with one of the single wheel affairs.
How do you find the resistance, is it very noticable, or marginal. Do you feel if there is noticable resistance, it offsets the heavier feel of a bike fully laden with panniers?
Also, have you had any experiences where you rate having a trailer has been beneficial to panniers?

Thanks