Well there is no "Easy Button" when it comes to migrating SPD workflows to Nintex. Even though they use the same SharePoint engine, they are very different platforms. Take for instance the Flexi Task. You will use this task action for almost all of your current task actions within SPD workflows. They perform similar functions, but relate very little. The details that you can control around a task process is of much more granularity.
Also Lazy Approval, State Machines, and other actions were not available before. You may find that the logic and operations actions are far superior to SPD that you may want to take the opportunity to adjust the workflow to use these features.
That is the main reason you do not find a magic wand to make this migration possible today. If you had one, you may end up keeping your workflow in the little leagues and never take advantage of some of the awesomeness before you.
Hope that helps,
Andrew
Hey Andrew,
Was afraid that was the case. Thank you for the input - sure I'll be back here soon enough.
-Greg