I can see that this subject simply entralls everyone.
I've heard back from a bunch of people on CN, and the two main answers I get are theses:
1) Go and order the Full Spectrum (UV/IR/Visible) clear glass filter from LifePixel and do the mod myself. It isn't hard, and with an external UV/IR filter it will still work beautifully for terrestrial photography - albeit with a slightly different white point. That's OK as I usually take RAW anyway.
2) Simply remove the existing filter and leave the sensor bare - i.e. do't replace the existing IR filter with a clear one. The argument is that an overlay filter will trap dust bunnies behind it, while a bare sensor is easy to clean (they are still covered in optical glass).
I like answer *1 as the clear Full Spectrum filter lets the autofocus still work. Without it the autoficusing systems go out of calibration.
So! Time to order the filter - US$95.00 plus shipping.