I've personally fixed many issues with email sorting myself with Gmail filters and so forth but it would be nice if I didn't have to have these filters and my client did it magically.
I hope it keeps my Google address book and my ability to send from a selection email addresses I own. Losing those would be a deal breaker.
Glider will pull in your contacts and address book, and other similar data to make the transition viable. Definitely let us know if there are other features you rely on so we can work on implementing them.
Import Export won't be very effective for me. I update contacts on a regular basis and the Google Address book keeps it synced to my tablet, phone, and Home and Work computers.
I hope it keeps my Google address book and my ability to send from a selection email addresses I own. Losing those would be a deal breaker.