Don't use a task killer.
Besides that, I think what's happening is that the OS is killing the browser process and it has to bootstrap itself when you switch back. I wonder if it is actually hitting the server or just grabbing a locally cached copy and rendering that. I'll try to figure that out.
Anway, I don't often see this issue. I use dolphin HD and I'm picky about what runs in the background. I pretty much use no widgets or other stuff that runs on boot. Theoretically, this leaves resources free so your browser can stay open.
Update: OK, just used dolphin hd to go to a page with a time stamp, went app drawer, opened google earth and played around a bit, went back to dolphin and the page was gone. After a couple seconds, the page came back...same old time stamp. This is good news as the page isn't reloading from the server, just re-rendering from local storage.