Newbie question regarding roms

[Vance14]

I have now rooted and am reading through some of the stuff on ROMs, but am having a bit of trouble finding what the major features of a given ROM are. I am using Launcherpro which gives me all the user interface stuff, and I would assume I would be using the same launcher with a custom ROM, so what type of "under the hood" features do the ROM's have in general compared to a rooted phone with stock Froyo and a decent launcher?

 

[scarryman04]

Mainly modded ROMs just have extra UI features. Such as changing the color on your notification bar or lock screen. They also have added features such as apps2sd where you can put any app on your sd card, take the clock out of your notification bar, things of that nature. Nothing really "under the hood" unless you get into custom oc'd kernels...the ROM I'm currently using has a performance section where I can set minimum and maximum overclock, and has a governor for your OC...but that is in my ROM settings.