With all these descriptions about how things tend to lag after a few days of operation or how after performing a reboot their phone response is back to normal, I'm getting the feeling that there's some sort of memory leakage going on.
Now, I don't know much about how these fine people go about modifying the android system or creating awesome themes like they do. I'm a computer tech by trade but I know very little about Linux, the droid is sort of my way of diving into the linux world. Taking a look at the android architecture layer on their SDK website:
What is Android? | Android Developers You can see that the application framework layer holds all the key components that allow the apps communicate with the system. Now agian, I'm not exactly sure what gets modified in these custom roms but logically I have to think that if changes are made to the components in that layer or in any other layer underneath the app layer, there may be some unforseen side effects when those resources are accessed by applications from the marketplace or wherever you get them. It is impossible for these devs to test every single app, every single widget on the market to make sure it works on their rom.
I agree with the OP that the Official rom is the most stable version around. And it is my humble opinion that people who don't have a working knowledge of the phone's operating system or at least is trying to learn (that is what I'm trying to do) have no business installing custom roms, or at the very least have no grounds to complain on the dev's thread that their "roms sucks" and gets laggy after a few days of use.
Everyone should keep in mind that the developers are not you. They don't know what you're doing with your phone personally, that's why results vary. The fact they actually take the time to answer questions on threads for something they made for free, aside from donations here and there, is nothing short of a miracle.