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...open Activity Monitor and select "All Processes" and then click on the "CPU" column header to see what's using the most cpu power. Also look at the memory columns, especially "Virtual Mem" to see what's using your drive a lot. Disk "memory" (Virtual memory) is much , much slower than real memory (RAM). With only 2GB of RAM, your disk may be getting a real workout! BTW, you can select what columns are displayed by using the View->Columns item in Activity Monitor. Near the bottom of the AM window there are some tabs that may provide some interesting info. In the newer versions, selecting the "System Memory" tab will give you an updating total size of virtual memory usage, Page ins/outs can also be important.
If you start up each of those primary apps and take a screen shot of DU for each one, you might recognize which one(s) are the most intensive users of memory and your cpus. "Free" memory might be interesting, also. If those numbers are quite high, post the image, if you can, or just report the CPU %, Virtual Mem sizes/amounts and "Free" memory numbers.
Just for grins, I'm now running Safari and Chrome with two different videos playing, Pages, Fetch, Mail, iTunes video, iStmbler (monitors web usage), PathFinder (Finder replacement), SpamSieve, URLM Pro, Photoshot Elements and Activity Monitor. In the back ground are DropBox, Growl, DefaultFolderX, Typinator, ClamX Security, a clipboard replacement, GlimmerBlocker and the normal assortment of Pref Panels. Some of those apps are really doing anything unless something is edited or created. During the startup and running of this stuff, I managed to get the Page ins up to 787.9
MB. Page outs have not reported anything, but that would certainly change if I did some editing/creation activity, I'm sure. VM Size is shown as 379.4 GB. These apps and the OS are using ~5.5 GB. All this shows is that with "only"
8 GB of memory, one can have a lot going on without slowing things down with Virtual Memory.
I'm suspecting that most of your Virtual Memory is being created when the apps are started. Each one you start requires many of the others to send stuff back to the drive so there's room for the 'new kid on the block!' And when any of those need to perform some task, they have to re-load it from the drive. And unless you replaced the mini's drive, it's probably running at 5400 rpm, that's kinda the standard for laptops and the lower end iMacs. Higher end drives are ~40% faster.
Obviously, having apps that are actually performing tasks instead of simply 'waiting' to be used will increase cpu usage. But most apps will off load as much code as possible if they don't need it to perform whatever they do the most. When they need that code, they will reload it from the drive (Page In). That's why they would then run slower, it takes a lot of time to have that stuff re-loaded into RAM. And the OS will probably require other apps to send more of their code to the drive (Page Out). That means when you switch back to those apps, they may have to do the whole Page IN/OUT routine, also. Minimum RAM is like disabling all but one cylinder in your cars engine. It will still run but not enjoyably!
BTW, Quitting Elements, Mail, Safari, iTunes and Fetch reduce the GB used to 4.5GB without changing the other figures perceptibly.