I have seen more than one Sharepoint intall crash so badly that the company was crippled for hours because they couldn't access their documents nor be sure they were working with the most recent versions. Having a regularly (as frequently as needed) exported mirror is a top priority for any SP-like application.

And, of couse, when you do realize SP is utterly awful when compared to its competitors, it makes the migration a lot easier.

I can easily imagine a migration from SP a couple years down the road would cost a lot more than the US$250K they are being offered to leave Notes (which is every bit as awful as SP)