Just a quick note, this might have been obvious to other more experienced users, but I thought I had bought some dead ATTiny85 chips on ebay. The first two had worked fine, and then the next three wouldn't respond. Then I got some brand new ATTiny84 chips and couldn't get any of them to work, so I knew there must be a trick.
The short answer it turns out, is that you need to short J3 on the USBasp. Mine didn't even have headers on it, so I had to solder on some pins. This makes it work for 1MHz chips, which takes 8x longer to write. Once the reprogrammable fuses are set for 8MHz you can remove this jumper and write much faster. This is most easily done by writing a program with the Arduino IDE or even just using "Burn Bootloader" which just writes an empty bootloader script and sets the fuses.
The chips should come from the factory preset to 1MHz and all the other defaults, but I guess the first two chips I tried had already been used, as I didn't need the jumper? I worried that the other chips might be dead, or had their fuses set so you couldn't write to them, and looked into devices for fixing them. I decided it was cheaper to just get more chips than such a device. So now I have a surplus!
There was no description of J3 on the USBasp silkscreen and there had been no instructions with the device. I had wondered what it did but assumed it was for special cases or to do with reflashing the device itself (as is J2).
I found this trick buried as a small note in an instructable, http://www.instructables.com/id/The-Idiots-Guide-to-Programming-AVRs-on-the-Chea/step4/Setting-up-your-not-so-micro-computer/
Hope this helps someone like me!
