I would like a trailer for grocery getting and other times when I want to take something a little bigger then what fits in panniers. The only time a trailer makes things harder is going up hill, because you have extra weight back there. I think the key is making sure you have low enough gears to allow you to gear low enough to compensate for the weight on hills. You also want to make sure you attach a safety flag to the trailer, this goes at the very back of the trailer and contains an orange flag at driver's eye level to indicate that your bike is longer then normal. Drivers can cut it too close and hit the trailer which is lower to the ground otherwise. You sometimes see these flags on 'bents as well which are lower to the ground.

Trailers come in two types, single wheel and double wheel, single wheel trailers can be a little tippy, if the load isn't properly balanced. Double wheel trailers need a flexible hitch so the bicycle can lean in corners while the trailer remains level.