When I started my family tree, I decided I'd better use the International Standard Date and Time Notation to avoid problems with e.g. different spellings of the month names, different order of writing dates in different countries (in some countries they put the month first, in some the day, which cause confusion when the day is less than 13) etc.
Today I got a tip - someone had a relative in common with me. Very nice, I thought, and proceeded to check the match out. Everything looked OK, except the date, which was "the other way around", i.e. the month had become the day and vice versa. When I checked all my other entries, I found this had happened to ALL OF THEM! When the day was a higher number than 12, the site had simply thrown out the date altogether (the software probably saw an illegal date, and couldn't handle that...).
This is, to put it mildly, highly annoying! All my date entries are now messed up, and I have to do all my work over again.
Why the heck don't you use the International Standard? It would be SO SIMPLE to base everything on this, and then allow the user to see and enter the information in whichever format he/she is comfortable with.
Now my family tree is badly contaminated with dates that has reversed month/day settings. No wonder my research has been so hard.
You simply can't do this kind of transformation on the web without notifying the user. Not only is it a bad assumption to do that the user has got things wrong, the behavior is also inconsistent. Would you correct the names of our ancestors too without telling us?
One of the golden rules for web designers is supposed to be:
"Never assume everyone on the web lives where you live having your customs. "
So why don't you please let us all know the answer to Torbjörn's question?