Here is a list of what we are loosing when moving to GitHub:

• no private branches (where we'll put our repository for papers?)

• no private wiki pages (where we'll put our todo list and referee comments?)

• no search in wiki pages (github proposes to do it from command line using grep)

• limited code browser (for example, no way to compare old and new versions of the same file, and yes, I regularly use this functionality)

• no way to adapt to our needs the interface of the code browser, wiki pages and issue tracker (for example, currently it's difficult to switch from code browser back to documentation)

• some information (formatting, dates, users) will be lost after migration of the tickets from trac to github.

• backup of github code repositories is more difficult (needs manual intervention for any new repository)

• backup of issues/tickets is even more difficult

• restore from backup is not clear at all