Well depending on which ROM your flashing, some offer UC(User Customization). What is UC? It is a feature contained in UC capable ROMs. A UC capable ROM extends initial customization to your SD card so you can load cabs and install XML files that are located there too. What this means is that once you get your customization scripts right, you can flash any UC capable ROM and all your apps and settings will be restored as part of the initial customization process whenever your SD card is inserted in the slot.
To find out more about UC go here:
http://forum.xda-developers.com/showthread.php?t=366337