If there are no holes in the top copper, then there's no difference.
Well, maybe not at the lowest frequencies (has to do with skin depth of the copper layer), but that shouldn't be a big deal.
You may find it's useful to carve traces out of the top layer, though. It's pretty easy with a utility knife, and it makes SMTs so much easier to use. Then you'll have to worry about how good your top-side ground is, and you may need to add vias to the bottom side (drill a hole, shove a tight fitting wire into the hole, solder it both sides) around important traces and ground paths.
It takes about as long as laying out and drawing and etching and drilling a proper PCB, but it takes shape while you're building the circuit.
Tim