How can I speed up the GUI?

Does your system has enough hardware resources? You can use light weight desktop manager like LXDE instead of Gnome / Unity. If you still prefer using Gnome / Unity then, you can use it without any effects (you can choose these options from the login screen). That is, Unity 2D:

• How do I install and switch to the Unity 2D desktop?
• How do I install LXDE / Lubuntu?
• How to revert to GNOME Classic Desktop?

You can try a basic or light weight window manager such as Lubuntu (openbox + LXDE), Xubuntu, or fluxbox. If you are running Unity, you can run it in 2d.

I have a quick guide on Fluxbox here :

http://blog.bodhizazen.com/linux/a-5-minute-guide-to-fluxbox/

You can find other, longer guides as well if you stay with fluxbox.

In general, of the ubuntu flavors, and performance of window managers :

Lubuntu > xubuntu > ubuntu > kubuntu

But, if you do a minimal instal, and install kde, and not kubuntu-desktop, kde is fast.

Ubuntu wiki Minimal Low Memory Systems

In my experience, with anything resembling modern hardware, changing window managers and turning off effects has little to modest effect on graphics performance.

Performance is most affected by the driver, the nvidia closed source driver performs better then the open source driver for example. As another example, the GMA500 runs gnome (2d), with all the effects I use (transparency, etc) faster on the psb_gfx driver then openbox with no effects using the uvesafb.

Other drivers can affect your hardware as well, including interestingly wireless drivers.