I run my organization's web site, which gets minimal traffic all year except for about 10 days a year, when we make announcements that a lot of people care about, so the traffic spikes.
Most months we'll do 200-300 MB of bandwidth, but at the peaks we'll do 3-4 GB in a day. And most of that comes within the same hour. I can't find out sure, but I'm thinking that as many as 3K-4K visitors may come at the same time, at the top of the hour when the news breaks.
I've been looking for a new host because I had some hacker problems at my current host. In looking for new hosts, I'm hearing a lot of different things about what I need to handle those spikes (shared hosting or a VPS).
On one hand, I've got shared now, and it seems to handle the traffic OK. It slows a little, but no biggie. I'm worried that I'm asking for trouble, though. I can't have my site crashing at these peak times.
If I want to switch to something that gives me a VPS, I found that DreamHost has a plan that lets you adjust the amount of memory all the time. That would be perfect, so I could use the minimum all year, and only pay for the extra on days I know I'll need it. My only concern with DreamHost is that the reviews don't seem to be as good as other places.
I also wonder if I should move at all. My site got hacked twice within a week, even though I changed the password. Now it's been fine. Maybe that was just an isolated thing and not worth the hassle of moving.
Depends where you're from. If you are dutch, I would recommend antagonist.nl or some else, though if your from elsewhere I dont know a good one.
What I DO know for sure, is that when the traffic most of the time is minimum it will save you money when you just stick to a normal host and not a VPS or dedicated. And the hacking; if its your own CMS I would consider checking your code instead of blaming your host, because most of the time the sequrity issue is you fault. Maybe using a different CMS if its unsafe?