[onemorepassword]

Relatively little. Yes, there are visible spikes if a site is mentioned on TV, but it's nothing compared to what a decent size mailing can do, or getting attention from a major website.

Even when I used to work for a major TV station and we did very strong promotion in and around well viewed prime time shows the spikes in traffic were nothing shocking.

Of course this says nothing about the long term effects.

[brador]

Mailing, you mean postal or email?

[onemorepassword]

Email.

And be careful with email mailings, especially during office hours. Apparently most people have nothing else to do but check their mail every minute and click on every link in it. Huge traffic spikes.