[jlokier]

One of the complaints I've had is that my mail had to be horizontally scrolled to be read.

One long line sounds likely to make the problem for that person worse not better!

That was a while ago though. Clients may have changed.

I'd love to know if someone has put the time into cross-platform tests for this sort of thing.

The only thing I'm completely confident of at the moment is that multipart/mixed text+HTML works for every client.