How much salt can I safely add to bread dough? I recently made ciabatta, which turned out very well, with a good crust and nice open crumb. However, I felt it could use more salt to give extra flavour. I'm aware that salt and yeast do not make good bedfellows (or should that be breadfellows?), so how much salt can I safely add to the recipe without compromising it?

FYI, the recipe in question uses 3.25 cups polish, 3 cups of flour, and 0.75 cups of water to 1.75 teaspoons of salt (I use table salt to avoid lumps of undissolved salt in the bread).
Based on experience and experimentation alone (I bake bread several times a week), I'd say to be consistently safe you probably want to max out around 3% in baker's percentages.  2-2.5% is much more common, but I've done as much as 3%.  After 3%, things got very inconsistent.  Sometimes it would work if the structure was just right, but mostly I got loaves that didn't rise well.

If I did my math and conversions to weight right, it looks like you're probably in the 2% range, so you should be able to add about 50% more salt.

EDIT:  It must be higher, but I'm not sure how high.  Bread Baker's Apprentice as a 4.2% Poolish Focaccia and other others in that range.  BBA seems to max out in the low 4's.