[Koha] Experiences with migrating from Aleph to Koha?

Dear Community! I'm writing on behalf of a library that currently uses Aleph, and is a bit curious about Koha. They want to know if there are any libraries that have made the switch, and what the experience was like. I guess this falls into two categories: - How smooth was the migration? - How big was the leap, in terms of functionality, features etc They would also be interested in which modules of Aleph were used before the change. If you answer me on or off the list I will forward the answers to the library in question, or put you in touch with them for further communication. Best regards, Magnus Enger libriotech.no