If I am running multiple tabs and navigate away from one or more of them for several minutes, once I switch back to a previously unopened tab, Safari refreshes it. Why is this? This is making it incredibly hard to accomplish tasks when in Safari.
Are you running out of RAM?
Open Activity Monitor and select All Processes and then sort by Real Mem to show you the process(es) using up your RAM.
Hopefully I can answer this correctly...
I have 8GB of RAM in my MBP. Activity Monitor is showing that I have USED 2.41 GB and FREE 5.58 GB.
I have heard that this occurs in the new version of Lion, making it act more iOS like.
You seem to have enough RAM, maybe it is just a bug. I have experienced the same in Safari, but on Mac OS X 10.6 Snow Leopard just yesterday, but I had two windows with at least ten tabs each open, though I didn't monitor the RAM usage to see, if RAM was the culprit, or if it might be just a bug.