Tim,
I insist that my customers pay escrow fees plus (at least) one day of billable time that I use to prepare, test and ship a package suitable for escrowing.
When I prepare an escrow package, I ship not only my source code, but copies of my development tools, add-on utilities, etc. I package everything up, with instructions, and ship via CD.
Some companies may insist that you ship an installable version of your development environment so a remote developer can rebuild your application and do a binary comparison between their build and your current production build to insure that you've shipped all the source code. If you need to comply with this requirement, make sure you add SEVERAL days of billable time to your fee schedule.
Malcolm