I often do not have luck with zucchini because the vine borers get them. This year I put Dipel [contains bt - see my gardening page for a description of that] on the plants as soon as they had secondary leaves. That seemed to help. Dipel washes off, so I re-apply regularly - especially since it's so hot and I have to water every day.
I'm pleased to report that I've had a good crop of zucchini this year. It slowed down after that week of 100 + weather, then picked up when it dropped down to the 90s. I'm guessing that it doesn't like to set flowers when it's roasting. Who can blame it?
This zucchini is Castata Romanesco. I got the seed at Baker Creek and I"ll be saving some to see if I can grow it again. I've planted it between a pattypan and a lemon squash so I'll have to hand pollinate if I want it to come back true.