Welcome!
I agree with takeshi said - do not use a task killer unless absolutely necessary. I uninstalled my TK 5 months ago, and never found a need to use one. The Linux kernel automatically shuts down apps not in use, and regulates the others.
Enjoy the Droid. I am a bad offender when it comes to switching phones (Went from a Centro to Pearl to Curve to Droid in 6 months), but it has been 6 months from that with my Droid, and I still love it. Although it's starting to be outdated, I have never owned a more rugged (dropped this thing 3 times, once on concrete from 3.5 feet up) or fun (especially if you get into rooting) phone.
My final recommendation is do not spend a lot of money on a screen cover. Most phones require it due to the delicate glass being used, but the Droid uses a product called "gorilla glass", which is many times stronger than ordinary tempered glass. I work in a dirty environment, and use kevlar/tar gloves (cut prevention); however, after having my screen cover off for 3 months, I have yet to have one scratch on my screen. My buddy scratched his iPhone 4 in 2 days.