There hasn't been any custom ROMs yet, haven't seen any posts regarding any that are WIP at the time.
PlayfulGod has already made a custom kernel that is overclockable to 1.6GHz but it hasn't been tested as of yet.
Also, currently nobody has even changed the recovery image, though PG has also built CWM for the device, and I hear rumors that there is a port of the recovery image from the Revolution, which is what the Esteem is based off of, but nothing yet.
I'd say that we can't really think custom ROMs until we have a working recovery image to apply it with and even then we'd need someone to build one. Hopefully we can get a working CM7 rom at some point!