Really? I always maximise my browser and usually dislike not having windows full-size on my screen. It just gets fiddly otherwise. Also I like leaning back as I surf, and I need a big browser window and 120-150% page scaling for that.
Using someone else's computer with a browser that isn't fully maximised irritates me, but I generally only see that on Macs. I don't think it's very common on Windows.
Everyone is different. I know a ton of people who always browse with 80+ tabs open. I find I fall into that weird trap sometimes too. Though because I have iChat and Twitter open, my browser is usually never full screen.
Using someone else's computer with a browser that isn't fully maximised irritates me, but I generally only see that on Macs. I don't think it's very common on Windows.