Mine curves down and a teeny bit to the left lately, which seems odd because I always spank right-handed (even though i'm left-handed). I think the curve comes over time from where you position it in your briefs...just naturally takes on that shape. I position myself straight downward so I'm guessing it just got used to curving around my balls. That's my theory at least. I do think an upward curve looks cooler...seems like it would be stiffer going in for some reason.
The curve's not bad if you use it correctly to stimulate the gspot. If it curves up, do mostly face to face positions. If it curves down, go with doggy style more.
If it curves to the side..... get a kama sutra book, cuz there's no positions that I can easily explain. LOL.
If you like blow jobs, coax your girl into a position where the curve will follow the line of her throat rather than curving up to the roof of her mouth. ie: curve up: 69, curve down: her between your legs.