We had done pretty much similar thing on our environment. We did a in-place upgrade from SQL 2005 to SQL 2008R2. We did had some road bumps when it automatically failed over to the node2 when upgrading node1 which is what it should have done. But for some reason the failover didn't succeed and we were stuck for a while. So my advice to you is before doing the upgrade/migration ;
-Have a good contingency backout plan.
-It is must that you test your Failover Clustering to work properly as planned. If you haven't tested your node failover , Do that. Don't miss this step as it is very important for the server to failover.
-Get your sys engineers , San Admin , sys admins involved so that if something fails you have some support.
-Have your SQL backups ready and up-to-date. You will need this if you have to built the Server from scratch if anything goes south.
Over all , not a big deal.
Best of luck bro.