Why did my homemade PCB turn out like this?
I get excellent results every time I use presensitized boards. Probably it depends on the PCB you use. I buy Kingston boards from eBay and they seem to be good quality. At least I've never had any issues so far. For etching I use ammonium persulfate. It's a white salt which dissolves in water to clear solution. Therefore it's very easy to control the etching process visually. Also it doesn't leave nasty stains everywhere. You need to warm it a little bit though (40C is probably enough).

You might want to look at this video. It's explanation of whole process I do every time.

http://www.youtube.com/watch?v=f_MCRcQdBQk