Some feedback.

I just upgraded a site from 1.2.5 to 1.4.0.4 in one go.
Only had to change a few deprecated functions in a custom theme.

Excellent guys !!!

Credit goes to sbillard, I had nothing to do with it...;-)

Thanks for the confirmtion. We do strive to make these jump upgrades work. Unfortuhatley it is just not possible to test each combination.