"Well, I may be wrong, but if you take residency in Eurozone, you pay no income tax".
You are wrong. See my post above .It applies.
In a past life I advised on tax etc and administrated many of the contracts that 'your' IT friends had. As such I know exactly what they are telling you. As I said before, it is based upon what they think they can get away with rather than what is their legal liability. That liability always rests with the individual and hence so does the risk of not meeting it. To be frank most IT contractors never really understood the way in which this liability arises, or maybe they just 'chose' not to understand.
"However at the time (don't know what the status is now), it was perfectly legitimate to avoid paying tax if you were a) non-resident in the UK and b) not resident anywhere else for more than 6 (or was it 12 - hell this was 17 years ago now) months at a time. So if you genuinely just got 3 or 6 month contracts and moved around for each one, then fine, no tax".
This is exactly how most contractors misunderstood how their liability arises. Not legal at all.
IR35 does not apply to this activity. In effect IR35 tries to establish a relationship between the individual and the person (client) they are working for on the basis of if you took out all the middlemen (Ltd co,agency etc) could the relationship be said to be the same as that you would expect to find between an employee and his employer. This to be distinguishable from someone who was supplying a service which was a business in its' own right. Its' quite complex ,but would not apply to this area of activity.