The sluggishness, in my experience, depends on several factors:
* Which toolkit is used (if any). Tk-based apps seem to be very quick, since Tk is pretty spartan and basic. GTK-based apps are okay. QT apps aren't quite as OK. Pure-X apps are zippy, but they're ugly as heck.
* Which WM/DE you're using. GNOME3 and its relatives (Cinnamon, Unity?) are sluggish as heck. KDE and GNOME2/MATE are much more tolerable, with or without desktop effects. (Open|Black|Flux)box are zippy, as are cwm, Emerillon, WindowManager, and virtually all of the tiling WMs. Enlightenment is zippy sometimes, but I don't think I've ever managed to get it to run without crashing back to a login screen within 5 minutes of use.
One curious thing I've noticed is that system resources have absolutely no bearing on UI zippiness. Whether I'm on a PowerBook with 512MB of RAM or a gaming rig with some Intel Core i9-867-5309-Quakemaster-Ludicrous-Gibs-Edition-whatever and terabytes of RAM with some NVidia GeFarce GTXXX 5-million-CUDA-core 8GB SLI monstrosity of a video card with hardware-accelerated 3D grass rendering, GNOME will always act like it's running on a God-damn ENIAC.
This is precisely the problem with Linux. Everyone wants to work on cool kernel-level stuff or daemon-level stuff; nobody wants to bother with the tedious, unglamorous last-mile work of actually delivering a polished user experience around all of that cool stuff.
That's another problem with Linux. "Linux" is a kit of 50,000 mostly-compatible little parts. If your hobby is assembling systems out of these parts, that's great; but it's less useful to you if you want to do higher-order work on top of an assembled computer system.
For example, tailing /proc files and compiling new kernel drivers shouldn't be a part of getting wifi to work anymore in 2014. It should just work. Of course, if you want to tinker it's great that you _can_ tail the /proc files, but you shouldn't have to. You should be able to turn your computer on and just have wifi, out of the box.
You can work with the GUIs for instance, but somehow they still feel very sluggish