I've installed FSR (force sensitive resistors) on all of my printers now. I developed a universal mounting system that I've used on Rostock Max, Mini Kossel, Kossel 250 and Taz 4 or 5 Cartesian printers. I print these in PLA but if you use a heated bed - and especially if you heat the bed to more than 60°C - you need to make sure the mounts are well insulated from the heater. The Rostock Max and Orion printers have a nice solution - a 1/4" thick melamine "snowflake" that the heater and glass mount to. This provides excellent insulation AND stiffness to get reliable triggering of the FSRs. I hypothesize that some of the issues I've read on the Web about unreliability of FSRs are due to two issues:
- The mounting system is over constrained or not assembled correctly and binds
- The glass build plate and flexible (silicone, Kapton) heater attached at three spots around the perimeter is too flexible so probes over the FSRs give different results than probe points between them (where the bed is suspended between the mounting points)
Make sure to address these, along with insulating the mounts, and you should expect good results.
The printable mounts and instructions can be downloaded from Thingiverse: http://www.thingiverse.com/thing:1335095