Why is my iMac (2.8.GHz Intel Core i7 w/ 4GBs RAM) using so much RAM?

Your memory use is not excessive. There is nothing unusual about those processes. I surmise that Firefox is running some Flash content, but the amount of memory it's using seems normal.

4 GB is considered merely adequate for Lion. OS X uses memory very efficiently and I wouldn't be concerned about what you're seeing.

When you begin to run into memory limitations it will manifest itself in an increase of page outs. When page outs become a significant percentage of page ins, it's a symptom of not enough RAM. What "significant" means is difficult to quantify, but 10 - 20% is completely normal. 100% or more is too much.

Here's mine: I have 16 Safari tabs open, some with Flash junk, and 13 apps "open" according to the Dock indicator:

By the way the number of icons in your Dock has essentially no effect on memory. Only running apps - the ones with the little dot indicator - might be occupying memory. Even that is somewhat of an oversimplification, since "active" apps may or may not have any active processes associated with them. It's all a function of how Lion manages its memory resources, and that is a whole new world to most of us.

With Lion, Apple is seeking to eliminate the system effects of whether an app is even open or not. Just another trivial detail the average user ought not to be concerned with, in their opinion.

If you want a cursory introduction to that fascinating subject, Google the Ars Technica Lion review that was written a few months ago. It may ease your concerns about memory management. If you are an experienced computer user, it will rock your world.

So we're in Beta of Lion, I suppose.

Nope, Lion is currently on 10.7.3, this is a production release and not Beta software. RAM is pretty cheap and simple to install. Look at www.macsales (OWC) or Crucial to spec out how much you can expand your Mac to and then upgrade the RAM.

4GB in today's computing world is not very much RAM.

So what you're basically saying is 4 GB is not much RAM to handle Lion and what it's using is normal.

Basically, yes. 4 GB is merely sufficient. I suggest a simple test - load as many programs as you can and observe the system response. You will find that you can push it pretty far before you notice any significant slowdown.

You did well to choose the i7 iMac. It is an excellent computer that will give you many years of service. Bookmark this page for 2018 or so and tell me how I did with my prediction.

Until then, definitely get more RAM. Your iMac can hold 16 GB and I recommend getting all you can. If cost is a concern then get two 4 GB modules. Your iMac has either two 2 GB modules or four 1 GB ones so add the two 4 GB and you will have 10 or 12. When you can afford it get two more 8 GB modules. Sell what you remove on eBay (though they're not worth much). I recommend memory from OWC or Crucial.

 > About this Mac tells you what you have, what you can get, and how to install it. It's easy and does not void its warranty.

Run Apple Hardware Test after installing the new memory to make sure it is recognized and passes all tests.