Is Domino 6 backwards compatible?

We are considering migrating the server from 5 to 6. Can anyone verify the true benefits, other than what is listed by Lotus on its website? Also, will there be any coding changes required? Is it backwards compatible? Thanks in advance.

Subject: Is Domino 6 backwards compatible?

yes, i was upgraded from 4.6 to 5.02, then from 5.08 to 6.5, up to now there is no issue except minor thing which we abled to fix it the moment we realised about it.