I placed an order for a synergy box last night, but this might interest you as a series of events;

1) Car has rear fuel pump replaced before purchase.
2) Checked over, dog slow, assumed MAF to blame, bought it anyway as intending to go down the Synergy route even before I had the car so not concerned, also got a hell of a deal.
3) Disconnected MAF, drives much better.
4) Washed MAF in Meths / Acetone cocktail, allowed to dry, reconnected MAF. At the same time performed the air intake mod (or my version of it anyway). Far more power than with MAF disconnected.
5) Like a PRAT I put 20L of unleaded into half a tank of diesel, caught myself, topped off with diesel and drove 10miles to my office (career limiting manouvre to miss the meeting regardless of risk to car) at low revs.
6) Drained a half tank (accessed under the rear seat squab), refilled with diesel, and have kept the tank brimmed since.

Now, I may well have damaged the CAT, but guess what? This was 500miles ago, there can be no appreciable traces of unleaded in the system, and I reckon (admittedly this is not empirical as I haven't scientifically measured power) that I'm feeling at least five extra ponies under my right foot than I had at stage 4 of the tale above........

This tells me that either I must have cleaned something out with the thinner mix, or I'm being naive by working on a single fault premise and something else is going on here..........?

i know of a few people that every now and then , put a bit of petrol in there diesels to clean it out(dont know if it works, but they say it does)wouldnt try it myself though.
dont worry about the CAT as its not the same as on petrol cars, so it doesnt matter if its even working on a diesel