The process of creating a text email from HTML is pretty wonky, it creates an illegible text email that takes quite a lot of time to go through and edit.
The ability to update the layout of emails is pretty time consuming and not "user friendly"
There are little things like, when you copy an email it takes you all the way out to main list, instead of instinctively knowing where you are in the databases. "Ease of use" is something that Silverpop could definitely work on, the platform not very "user friendly" or instinctive.
The reporting functionality is my LEAST favorite part of Silverpop. You can not pull reports based on many different factors, that should be a "no brainer" when setting up a reporting system. You can't customize your own report, you can't pull based on a title, you can't pull based on send date etc. Maybe I just haven't figured it all out, but it is complicated, time consuming and not easy to use.