There are most probably some such how-tos in the net already, but it might be helpful to have some migration guides available here and tailored to Ubuntu's charasteristics.

Partitioning, accessing file systems, multi-booting, sharing/migrating personal or application data, reusing Linux settings and /home partition from another distro etc.

Perhaps those who've already dunnit could also share their hard-earned wisdom and useful tips?

Avanti Ubuntu!