Using the Dev team method should be fine. I used it on my MacBook Pro and I jailbroke my phone in less than 10 minutes or so. It was pretty simple.
Find a good instruction or better yet, find a good YouTube video which guides you through the process.
Firmware 3.0.1 works fine, just make sure you download all the necessary files.
My sole reason on jailbreak was for SBSettings. I think it's probably the most useful app. I don't bother with the theme changes or navigation tools. Just SBSettings was worth the jailbreak.
I turn on and off 3G often and use WiFi whenever I'm at home or office. Same with Bluetooth and Location Services, I constantly go back and forth between switching on and off to have my battery last a little bit longer.
But, my girlfriend who also owns an iPhone, doesn't bother with it. She just keeps whatever setting I put for her and doesn't switch around. For her, jailbreak was unnecessary.
Jailbreak is for someone who requires or wants "special" things outside of what an iPhone offers as is. If you've just gotten it, try using it for awhile without jailbreaking it and see if you really need it.
Besides, (I don't know when, but) iPhone OS 3.1 should be coming out soon. At least wait for that.