I usually do both sides but one side should be fine.
Does it actually help to be a circle or any closed loop?
What type of installations do you do? Sensors? Motor drivers? High current LEDs?
As far as what I've already got in mind, high current LEDs, IR receivers, keypads, and rotary encoders will be common. I want to play with stepper motors at some point, but I have nothing in mind so I'll just get a shield eventually.
But I'm hoping to produce a platform that will be useful to others. The main advantages to my board will be the perfboard area and it will be routed to fit a standard, easy to get enclosure which has a battery compartment and optional IR panel.
Also, what's your favourite perfboard pattern? I'm planning on rows of 3 pads connected with power down the sides of the board, but 2 pads also has some appeal. Both ways give me 1 hole on each IC pin.
My original plan was power running between every grouping of 3 like the cheap radioshack boards, but that spreads everything out so much and it's a fairly compact board because it's a small handheld enclosure.