I know the solution "move sheet to the most left" to make it default when opening spreadsheet.
Thing is that I got one spreadsheet per week, and it's quite messy to move around like that, plus it will be much more user friendly.
Something similar to this Google Apps Spreadsheet open specific sheet based on current date (Month)
Weeknum is a rather new function in google docs, so I haven't found anything else googling around.
