I've been working on a horrible EE1 installation and bring it into EE2. Unfortunately it was one of those sites that decided to use Gypsy, oh and Structure and just to make things interesting, MX Uni Editor's file field.
The upgrade went relatively smoothly actually, although Gypsy was used throughout there were only a handful of channels so was able to just have 1 field group in the EE2 site and share it amongst channels.
The Structure upgrade went smoothly also.
Where we fell down was the assignment of images and attachments to entries.