We have been "converting" to Evo for several months now.  The change has been remarkably easy.  Here are the advantages we have seen:
 
1) We are now able to email .rtm forms from within DBA.  This has allowed us to send invoices, acknowledgments, and quotes much more easily.
 
2) The screen size is larger  
 
3) ** BIG ONE** You can have multiple screens open at once.  This allows you to be in the IN-A screen while printing a BOM or switch over to SO-A.
 
4) There are user login specific transactions.  This has helped us since we have several people who post to the GL and sometimes we need to know who did what.
 
5) You don't have to get rid of classic DBA.   We have users with two icons on their desktop: classic and Evo.
 
The downsides are:
1) That you have to set up new .rtm forms for many of the applications.  This was alot of work initially.  Especially if you have heavily customized forms.
 
2) You have to set up each user one at a time (this also helps with implementation since you can pick and choose who you set up)