Day to day:
1 : taking place, made, or done in the course of days <in charge of day-to-day operations>;
2 : providing for a day at a time with little thought for the future <an aimless day-to-day existence>
http://www.m-w.com/cgi-bin/dictionary?book=Dic tionary&va=day-to-day
happening every day as a regular part of your job or life:
day-to-day problems/responsibilities
http://dictionary.cambridge.org/define.asp?key =19740&dict=CALD
This is used, for instance, when someone wants to express that he barely has enough to make a living and it is like "he lives from today to tommorow".
Another usage would be when expressing that nothing can be steadily learnt too easy or too fast, so it is used like "nothing can be learnt from today to tommorow".
"One day at a time" is a popular expression to describe the way to cope with a difficult situation that will exist for a long time or forever.
You can also say almost the same thing exactly in English. "After the money ran out he lived from day to day."
http://www.phrases.org.uk/bulletin_board/22/me ssages/274.html
day-by-day: taking place each day; daily: a day-by-day account.
http://www.infoplease.com/dictionary/day-by-da y
of or belonging to or occurring every day; "daily routine"; "a daily paper" [syn: daily]
15:12 Tue 31st Jul 2007