Email Marketing Service Providers? Or... DIY

I've done my research on Email Marketing. However, I'm confused on a few things I hope someone could clarify on. Do I go through an email marketing provider?

I'll be handling a rather large list and I don't want any restrictions as to how many emails I can send in a month, year, etc.

I'd like to use Interspire's email marketer to handle this for me. However, do I install something like this in my BlueHost with everything being dandy when it comes to sending mass emails every month? Do I need a Dedicated server for SMTP?

Since you are on the topic of emails ...

I would like to ask if those "buy bulk email list" sites really work ?

Do you get your money's worth or should you stay far away from these sites ?