I recently migrated a clients site from Joomla1.5 to Joomla2.5 and would like to share with you some of the issues I ran into.  Essentially the migration was a success but only after a lot of extra work trying to recover from poor decisions along the way.

As far as I know there are 4 ways you could migrate your site:

1. Manually table by table using the process detailed here: link to joomla migrate
2. Using the new JUpgrade Pro Restful methodology (Sounds great)
3. Using the older Jupgrade free utility (doesn't sound too bad)
4. SP Migrate (Another Commercial App)

During my migration, I used 2 and 3 and a bit of 1.