I've spent the last couple weeks upgrading 2 of the largest Venture database in existence. One took 6 days, the other 7 to convert everything, but baby was it worth it!
One of the biggest pain points of large Xinet installs databases is performance- to increase performance when you have Millions (or tens of Millions) of records, you need to 'index' things you search on. In the old version large sites could take a week to drop, repair and recreate the database should something corrupt (and things do corrupt- if someone kicks out a power cable, you're gonna break MySQL tables).
Last week I put an index on the file table of one of these GINORMOUS sites in under 4 hours. Under 4 hours compared to 3 or 4 days! Oh, and during that time? Venture was usable.
That's just awesome.