I myself am in the midst of QA of software (web site) I've spent the last year writing. It's all well unit-tested but there's plenty more integration testing of the new functionality and worse, regression testing. Ugh.
There's no one else available to test (well, there's another dev in the same boat as me). I firmly believe that I'm the worst tester of my own code for all the reasons already stated. Other Dev and I will test each other's code to the extent possible, but that will help only so much.
I have a plan for today: I'll find a good podcast or something, one that will demand my attention (maybe In Our Time). I'll try to find a sweet spot where I'm giving 5-10% of my attention to my web site interactions. I figure that if I make sure to simply continue interacting--even if only randomly--I can approximate the mind set of the typical user. In the meantime I might learn something from the podcast or at least be somewhat entertained. It's win-win.
I'll let you know how it goes.
The decision doesn't have to be logical; it was unanimous.