I don't think anyone would recommend under 25ft of 1/2" copper tubing for a 5g batch, though many/most homebrewers probably don't use a wort chiller at all (I'm talking about those not as "in the know" with internet forums and such).
I've been using my kitchen sink, and am thoroughly displeased with using it to chill 5g batches since it takes forever. My next brewing $100 is going towards a plate chiller off ebay from Dudadiesel. It should be the absolute most efficient way to chill my wort, and at that price, the most efficient means of chilling wort by price. I was going to get the smaller 30 plate chiller, which is around $85, then spend another $20 or so getting fittings to hook it into the sink.
My biggest reason for such a high-efficiency chiller is that in FL the ground water temps are usually in the mid 70s during the spring summer and fall, and over winter up in Tallahassee they'll go down to the 60s, but at my home in South FL, the groundwater will be in the mid 70s 24/7/365, even when it's 50 degrees out.
Bottled: Year old Hefewisse
In secondary or aging: LHBS DFH 90 minute on-the-fly-made clone recipe
Next up: Thinking either deepsouth's 60 minute IPA or a nice quick blueberry wheat (Blue Paw clone) to end the summer with
I envy those of you who don't have to make a concerted effort to keep your fermentation vessels under 75 degrees....