There are three things being discussed here:
borderless windows -- I've no problem with them and have used them myself.
hooked window borders (like is often done with Aero Glass and, believe it or not, pre-Vista WM as well) -- This has legitimate uses, like when PS or Chrome uses the titlebar region for tabs when maximized, or when certain systems programs add buttons to the titlebar.
custom bordered windows, for lack of a better name, where the application draws its own borders for the windows. -- This is where I have a UI design problem. Such programs do exist, and are beautiful. I've written a few myself. And believe me, there's a
whole lot more to it than just drawing some buttons and implementing a few click-n-drag events if you want your users to feel at home.
Any decent image viewer will know how to resize an image with a properly-chosen resample filter -- part of an image viewer is the ability to zoom in and out; not just 1:1.
I use IrfanView -- it behaves very nicely. Press Enter to go fullscreen (borderless)/windowed (borders). When fullscreen, press F to cycle through the zoom options: starts at 1:1, match to height, stretch fill, match to width, best fit. Press Esc to quit.
http://www.irfanview.com/
It's Windows native, but works just fine on Linux with WINE.