Kirk McElhearn, writing for Macworld:

Right now, my iMac’s uptime (the time since my last restart) is nearly four days. And Safari is using 6.81GB of RAM, by far the largest memory hog on my Mac. The app itself is using about 1GB, but each tab, each window also uses RAM. You can see this in Activity Monitor (located in /Applications/Utilities), by selecting the Memory tab.

And:

As you can see [in the image in Kirk’s original post], the most egregious RAM user is Google Docs, which requires more than 500MB RAM for a single, blank document. Open a few more Google docs, and you’ll see that number quickly balloon. (It’s not clear whether this is Google’s fault or Apple’s fault.)

A lot of this memory usage depends on how long the pages or tabs have been open. If I launch Safari on my 12-inch MacBook, and open the exact same tabs, it only uses 2.8GB RAM. Of course, if I leave them open for a long time, that RAM usage will increase.

I fired up Activity Monitor on my Mac and tapped the Memory tab. My Safari only used 321MB (Less than 1/3 of Kirk’s 1GB).

I then created a new Google Doc blank document which used 193MB (again, much less than Kirk’s result), and added more Google Doc documents, each of which weighed in at slightly less than the original.

I don’t doubt Kirk’s results, but I suspect that there’s more here than simply Safari being a memory hog. It’d be interesting to see a more controlled experiment, loading known pages in a controlled environment after a fresh restart.