I ride mostly road and use a Serfas Cosmos Plus I bought late in '06(apparently just before they stopped making helmets). I assume it's a road helmet and it has a visor. I considered it personal preference to wear or not to wear the visor and I've never felt a pull from the wind. Even ripping down hills... but then, I'm tucked in and generally whipping past my featherweight companions.
No, I don't believe it's ever slowed me down, but if it has, I'm sure it's only been on the climbs...
Actually, I love the visor for keeping the sun out of my eyes and it's got a big cool factor....
In the woods, same deal. In fact, I'd find the only advantage to a visor in the woods is clearing branches(if they didn't get stuck in it), but that's what glasses are for, right?
The helmet has served me well and seems to have come through a spectacular crash in RW on Sunday that knocked me silly and left me with a touch of whiplash and an almost certainly cracked rib.
So, The helmet is still solid and shows NO signs of physical damage(but, seriously, my head does) Do you think I should replace it anyway?