Two years ago, I bid a sports bar/restaurant. Looked at the job site and got prints on a Monday, and faxed the proposal the next day. By the next week, I hadn't heard anything, so I started calling. In another 2 weeks, I was calling the guy 3 or 4 times a week, getting his voicemail, leaving messages. I implored him to call me, one way or the other. I had other jobs I was looking at, and didn't want to overbook myself if he was serious about wanting me.
I got to the point where I felt I was harassing him, leaving so many messages. So after a couple months, I gave up.
He called me up about 4 months ago, asking me to start the next day. he would be more than happy to sign my proposal and give it to me when I arrived. I kind of chuckled (especially since this bid was figured before the 500% copper price jump of 2006), and told him to look at the bottom. "This proposal shall expire 30 days after the date submitted".