We have lots of lefties in both my family and DH's family (including DH). I think "bad" handwriting tends to be more of a gender thing than a handedness thing. I think females tend to care and practice more.
It's definitely true that it's a world made for righties, especially with school and office supplies. Even so, I'd love for DS to turn out to be a lefty. Generally speaking, lefties have lots of natural abilities and advantages like spatial visualization (PP's mention of architecture is a perfect example), ball sports, eye-hand coordination, etc.
Of course, that could just be my personal jealousy speaking. I'm so right-hand dominant, it's pathetic!