I am assuming you have had your Droid 2 for a while; and have installed a lot of applications on it. I also assume that it is out-of-warranty.
Performing a factory reset will remove all your apps and data - and without apps to run, yes your system will feel faster.
However, as you add more apps over time, it will slow down again. Some apps like to run in the background, silently using up your devices available RAM.
From a quick search, I found that the Droid 2 comes with standard Motorola Bloatware. This software runs (and uses RAM) even if you have never launched it.
Since you are probably out-of-warranty for your device, you can root your it without fear. Software like Titanium Backup can "Freeze" the applications so that they do not run, allowing more RAM for you and your apps.