Please read the sticky post about how to report a bug.
Alright, just did. Sorry about that.
What video card and driver are you using?
The integrated graphics card on the second-gen Intel i7, the "Intel HD Graphics 3000". The exact processor is the 2670QM. The driver is the one used by default in Ubuntu. I'm not sure how to find out what driver is being used.
Also, there is no software running in the background besides the Dropbox app. The only MegaGlest setting that I have changed from the default is the resolution, from the default 800x600 to 1366x768, which is the exact resolution of my screen. I just reverted it to the default, and there is a noticeable
decrease in the amount of lag when clicking and dragging, but it's definitely still there.
Let me know if you need any more information.
Edit: Ubuntu's System Settings lists the graphics driver as:
"Intel® Sandybridge Mobile x86/MMX/SSE2"