Can't flash ATTiny85 with Arduino as ISP anymore

Using Arduino Avrdude, stk500, Bootloader issues
13

I can also vouch for TinyCore and an Arduino as ISP.

ergus:
I am using an Arduino uno as a programmer (ArduinoISP...) (snip)

It is somewhat confusing, but when using an Arduino as an ISP programmer, you want to use the 'Arduino as ISP' option rather than "ArduinoISP' (even though you load the 'ArduinoISP' sketch onto the programmer...).
This is what the 'ArduinoISP' programmer option is for.

ergus:
attiny85 arduino
===== =====
1 10
4 GND
5 11
6 12
7 13
8 VCC

Plus a 10uF cap between the arduino's reset and GND.

Have you tried swapping the MOSI and MISO lines over? The USI hardware that the ATTiny has is a bit different to the standard SPI hardware on the full-sized AVRs and it handles being the slave differently.