Feels a little weird saying this, but your penis sounds alot like mine, madmike. :p
Mine curves slightly downward, too, and has the vein on the left that pops out during an erection (not exactly "curled up" though).. I would say don't worry about the vein, but:
If there's a bump in your vein, see a doctor right away! It could be a clot or something else. It's probably not normal if it's on your vein - if the bump's away from your vein and white near the base of the penis, it's probably a hair or a whitehead.
You really think it's a problem? Maybe I got my wires crossed somewhere... With your post or madmike's. I've always just looked at it as like the veins on my hands/arms that pop out.