jethrotul

Virtual server is the physical server virtually divided into accounts, all the resources (disk space, RAM, bandwidth) are shared by all clients hosted on the server, and as soon as the resources are overused on one account the rest of clients may suffer.

Even buying 100 sites from one hoster, you may have them on different servers, which is both bad and good. it's good as it will allow you not to keep all your eggs in one basket, so if one server is down, the sites from other servers will be still available. What's bad about it is the process of administrating your sites gets more complicated.

You can search for good VPS providers on WHT, one of them is myriadnetwork.com.

swazi

You can do serious things on the shared account as well, what you are really limited in are your resources and freedom, but if the package allows you to run the site and the uptime is 99,99%, you can do serious things and cut down your costs.
I second myriadnetwork.com services when it comes to VPS. Their business ethics is great.

solyaris

Dedi helps you to control everything on your server. But I think it's better to have a fully managed dedicated servers though you have to pay more for that.

etrader

Dedicated server is a great service

but it is only needed for big site

I emphasize really big sites

The number of such big sites across WWW should not be more than 10,000

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charlesgan

dedicated server is better uptime and speed. thats the real concern.

shared hosting, the downtime will be more, due to sharing environment. someone else might overuse the resource in given time. thus causing others to running slow.

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amigo77

And it must be the host's concern to watch not to have overuse on the server.