Im starting a lotus/domino to Exchange 2007 migration. What are some best practices in doing this?

why?

There are various resources on this information but it comes down to plenty of planning for interoperability and how accurately you need all information carried over.
You can use the inbuilt connector to provide connectivity between the two systems if not all users are migrated at once and also provide basic migration facilities.

Also Domino is more than just mail so are there applications or customised templates to be brought across.

Also can use DAMO if outlook with all bells and whistles required.

But as I have found some companies are making a decision based upon market trend or justification of centralisation without actually looking into the real technical ROI or TCO.
As admins we can but do as asked on occasion.

To the OP.
I would recommend a test bed system with domino and exchange to test migrate so you can see potential limits to migration and communicate this to company before proceeding with main migration.

There is nothing technical about ROI or TCO.

It is just money.  As is often the case politics is more interested in image and perceptions than a solid fact-based smart decision about funds.