Eliminate "Bloat"
This is all the stock junk that Motorola puts on your phone such as Blockbuster, Kindle, Need for Speed, etc. Many people believe that by removing this you will see small increases in performance.
Root Apps
Take screen shots, get rid of ads, do full system backups, use a terminal emulator... there are really tons of things you can now do with your phone after you root.
Overclocking/Underclocking
After rooting your phone you have control over your processor speed and even the voltage used to power your phone. This means that, in theory, you can increase your device's performance and decrease the amount of battery used.
Custom Roms
After you feel comfortable with "hacking" your phone a little bit, it's time to move on to the good stuff- roms! Many roms provide speed, performance, and eye candy. Think of this as a different operating system for your phone- like going from Windows XP to Windows 7. Liberty is a very popular one around here for the X.
We're a growing community that only wants to help you out. Don't feel scared to ask!