Not necessarily.
Rooting only gives you superuser permission to do things you wouldn't otherwise be allowed to do. One of those things is to use an app called Titanium Backup to make, oddly enough, backups of all your apps and their associated data so you can transfer them to other ROMS. You can also, through the recovery portion of the phone, make an entire system backup called a nandroid backup. A nandroid is a complete system wide snapshot of the phone at the time you made it. I would highly recommend you do that after you've rooted before you do anything else. You can then do pretty much whatever you want and if it goes wrong you can just resotre the backup you made and *PRESTO* your entire system is back the way it was After the nandroid is done you can use Titanium to make a backup of the apps, either the specific ones you want to keep or just a batch backup of all of them. Then, using Titanium again, you can go through and delete the crap you don't want like all the VZ garbage, Teeter, pretty much anything. Be careful though, it will delete anything and I mean ANYTHING. Make sure you know what it is before you blow it up.
So, you've done all that and your running stock, rooted, and de-bloated, now you want to try out a ROM. Here's the process I use, I first make backups of my apps through Titanium, not all of them just the ones I want to bring over to the new ROM. Then make a nandroid backup just in case either the instillation goes wonky, or I just don't like the ROM, it's buggy, or maybe its just not what I thought it was going to be...this way again, I can just do a restore and its like nothing ever happened. After that flash the ROM. When its up and running just re-download Titanium from the market and there you go, you can now restore your apps and data. I try to not restore app data from ROM to ROM with a few exceptions like Angry Birds and other apps that I don't feel like starting from square one on.
Long answer for a short question but there it is...enjoy.
Oh, and if you do somehow manage to "brick" it, you're not entirely on your own, we'll all be here. I've had plenty of people guide me through my first rooting experience and ROMing experience on my Inc when it first came out. I was a bit nervous but the benefits of not having Verzion's garbage to put up with outweighed the risk for me.