Was looking at your code, alvarojusten, saw the function to represent the day of week as a string. Don't know if you noticed, but all the clock does in increment the day of the week by one (rolling from 7 to 1) every time it hits midnight. It does *not* seem to have any fixed association between the date/month/year and what day of the week it is. Convenient in some ways as you are perfectly able to define 1=Sunday, 1=Monday... or 1=Thursday for that matter (if you can get the hang of Thursdays...).
Similarly, it is perfectly happy to let you set the date to Feb 30... and then it continues to the 31st. Seems to know if the current m/d/y is the last day of the month -- and if so, it will roll to the next month at midnight. But it won't force the date to be valid for the month/year.
I didn't read about the day of week in the datasheet and don't know if DS1307 have calendar capabilities yet. If yes, so I can determine the day of week based on year, month and day. If no, it is just another information we can get (it'll increment from 1 to 7 for us each 24 hour) if we set the right value.
I'll add to ToDo of the project the test of calendar capabilities such months like Feb etc. - I don't know what DS1307 stores if we add a date that "does not exist". Thanks!