I have heard of Custom ROMs and Custom Firmware, are they the same thing? If not, whats the difference?

Possible Duplicate: Where can I find stock or custom ROMs for my Android device? I have found many custom ROMs for download. But now I want to use the official ROM for my phone. Is there any way to do it without a NAndroid backup?

What can a custom ROM provide beyond rooting that I can't get by downloading an application?

Can anyone that's used it list the relevant benefits and drawbacks? I'm actually more interested in the drawbacks and limitations because its not hard to find praise for it. Edit: Ooops, I forgot to mention, original Droid currently running Android 2.2

I want to try different versions of the Android OS on my HTC Hero (namely 2.2) but be able to revert back to the stock image. What are the steps required to do this? How can I extract the stock image from my handset? I am on T-Mobile UK if that makes any difference.

Possible Duplicate: Where can I find stock or custom ROMs for my Android device? I recently bought a Samsung Galaxy 5 (model number GT-I5500) and I'm new to the android world. I'm not satisfied with the performance of the GPS on my cell phone so I thought it would be interesting to use a custom ROM to see if it improves a bit. Anyone knows of a ROM that was tested in this model?

I'm looking for a good comparison of custom ROMs' features and quality. I would prefer a comparison that is actively maintained.

I've got a Droid Eris that I've loaded the CELB Froyo 2.2 Rom, which is based off Cyanogen Mod 6. I know before that ROM Manager was basically useless with the Eris but I was wondering if it works now.