How to Survive a Ground-Up Rewrite Without Losing Your Sanity(onstartups.com)
onstartups.com
How to Survive a Ground-Up Rewrite Without Losing Your Sanity
http://onstartups.com/tabid/3339/bid/97052/How-To-Survive-a-Ground-Up-Rewrite-Without-Losing-Your-Sanity.aspx
If there is a good tests infrastructure re-writes can be done with a heck of a lot of confidence. Plus there is the benefit of breaking the re-write project up along test lines which helps in not creating the pressure for a, "huge one-time switchover".