Nonono, bulk e-mail is definitely not a good idea. Many people mistakingly feel that if they can get their word out to the masses, people will visit their site. The problem is that most people feel that businesses who resort to spamming tactics to generate traffic almost always aren't businesses worth their time or money. It really gives a negative opinion, IMO.

Sending out e-mail to prior clients is another story. It must still be done very tactfully and very tastefully and, of course, as rossbliss said, provide an unsubscribe link. Opt-in lists are the best.