I didn't need one myself, but I've always found these to be extremely helpful. And that goes triple when travel might be involved for some guests. It's so helpful to have a "travel" section, where you give them info on airport limos (assuming you can't pick them up), hotel rates and contact info, etc.
On registries, this is controversial, but I personally don't have a problem when it's handled discreetly. By that, I mean the registry would be one small part of the site, and then when you send invites, you can discreetly say "For further info, please see our site at xxxx").
It shouldn't be an issue for showers, because the hostess is perfectly free to list the places where the bride is registered. In fact, she *should* do so.
PS - I totally disagree with that "tip" about website info being on STDs. All you're doing with an STD is giving them the date of your wedding. (I realize you're not doing them, but that was a strange thing to say!).