Fix templates to be more user friendly - most templates in these solutions can easily be changed, but these are hard coded and use image files instead of background colors. This applies to both email and landing page templates. I've used basic solutions like Vertical Response and iContact, and more automated solutions like Manticore, and have yet to have as much difficulty as I had with the LeadFormix templates. Also incredibly difficult to use on a Mac.
Support is in India and takes several days to respond. For instance, I had a 15k e-blast go out where the email opt out wasn't properly working. It was supposed to go out in batches since we knew LeadFormix always had issues and instead went out all at once, despite support assuring it had been cancelled.
It's fairly expensive in the face of other more robust solutions - their workflow is prehistoric in set up.