A few days ago, I started a similar thread on the Lucida mailing list at TUG. Karl Berry said that they'd discuss and look for a method to achieve a consistent look of braces in Lucida.

Thanks for telling about the strut=no option. I'll try it this weekend, but I think it will solve my problem for now. I'll try to remind you of the mathcases macros... We'll see ;)

Tobias