I run an IPB3 forum that gets quite a bit of traffic and being on an 'unlimited' shared hosting plan, I'm occasionally concerned that I may receive a notice that I'm using too many resources. I've just found where I can see what my CPU and memory usage is but I don't know if these numbers are high or not. Can anyone explain this to me? What exactly does it mean? What's the 'safe range'?

There is often some confusion when someone signs up for a hosting account that lists "unlimited" and then receives an email that they are going over resource limits.

The unlimited refers to bandwidth and storage and usually when a "high usage" email is sent, it is not due to storage or bandwidth but is instead due to Memory and/or CPU usage.

Bandwidth :  The amount of data that transfers between two computers. (LP can always purchase more bandwidth)
Storage : The actual storage on the server/hard drive. (larger hard drives can be added)
Memory : The amount of RAM on a computer (generally comps/servers can only have so much ram)
CPU : The processor on a computer. (To increase this, generally gotta replace a server)

Since basic hosting accounts are on shared servers where multiple accounts are on a server, all resources are shared between the individual accounts.

Generally you want to keep memory and CPU under 1%  (industry standard) which is enough for most basic sites.  If you are constantly going over this, then it may be recommended to try a VPS server , unless its really high in which case you may need a Dedicated server.

With a VPS server, this is still a shared type server however there are much fewer accounts per server and so each account can be allocated more CPU/Memory resources.

With a Dedicated, you are the only one on the server, and you decide when setting up the amount storage/ram/cpu on the system depending on the plan you use, and you can use these fully.

I'm getting warnings all of a sudden for "high usage," like a lot of other people. In my support ticket, someone said, "As you already know, this plan comes with unlimited resources (such as bandwidth, disk space etc.), so we don't have any limits on the CPU and Memory usage either." So is it unlimited or not?

And is LP looking into the possibility that something is wrong on their end? My traffic has been fairly consistent for three years, and now I'm suddenly getting warnings about my memory usage.

  We're moving to a VPS Pro Plan. We have a better understanding of the situation and the high usage CPU/memory warning.

It came down to this: we were on a shared server on a budget business plan with many other sites sharing a server. Our site consumed more resources than most on the server. Generally speaking, we were getting between 3,500 and 4,200 hits a day, 11,000 pageviews and up - a decent volume of traffic and a successful website. Now lets say there are 400 people on a shared server (when really we have no idea how many there are) - but, we are one of the top resource hogs: it's part of the plan to send out a warning notice. Yes. We had traffic similar over the last few years, but lets say that perhaps they have reached max capacity on that server and we were part of the straw that is breaking the camel's back. So, they send us that notice and we take issue stating our hits have not gone up because we don't get it. We freak out. Because we feel like we have squatter's rights. LOL. Which is a great analogy. Anyway, we don't want to pay more. But, now we get it. And, we were lucky that we didn't have to pay the larger sum of server hosting for the last several years.

We're in the midst of moving to a bigger place with more room to grow.

Interesting. Except it doesn't work when you have a dedicated ip address.

We're talking about high CPU usage on the web servers, not our personal computers.