No, but I have had the unfortunate pleasure of a steel triangle separating from an alu downtube (chemically bonded originally) when I used an old Raleigh Technium for touring. I can't recommend Techniums for this reason.
I know there was one other person on these boards did mention they had a rack mount re-welded -but I'm also of the mind that given the cost and time involved in re-welding (e.g. finding a good welder, paying for a good paint job) I'd not have any problem using an alu frame as probably the costs are going to be very similar unless you have a really boutique frame. I know this isn't necessarily true either, but I'd also have a problem riding a bike knowing it had to be rewelded as well.
I'd also be interested about people's experiences with having to have frames rewelded as well.