I just watched the newly released DVD of the Star Trek movie, and I noticed that the stardates are different from the original series and its spin-offs.
For instance, Kirk was stated to be born on stardate "twenty-two thirty-three zero four". Other stardates are in the form nnnn.nn. According to Memory Alpha, which quotes one of the screenwriters, the first four digits represent the year, and the decimal represents the ordinal day of year, from .1 to .365, so the stardate would be written 2233.04, which means that Kirk must have been born on Friday, 2233 January 4 CE (MJD 136649). According to the official website at startrek.com, he was born on 2233 March 2 (MJD 136707), but the stress of battle could have caused premature delivery. Other sources give different dates for this and other events, and I don't think that there is other date that is "canon", but a canonical stardate for his birth is 1277.1, from his very first episode.
The original five-year mission is usually assumed to have started around 2264 or 2265, but in the movie has the main events taking place on stardate 2258.42, or 2258 Feb. 11 (MJD 136687), apparently during Kirk's third year in the Academy, although that would make him 25 years old, and startrek.com puts his years there more believably as 2250-4.
So now we have a completely different sort of stardate, which is simply an ordinal date similar to that of ISO-8601, e.g. stardate 2233.04 = 2233-004. This makes them easier to use than the original stardates, which really made no sense, although now they're more likely to get in trouble by tying events to precise dates. And there is no mention of the time of day, which is presumably represented like our military time, rather than as a decimal time. I think I'll stick with the original stardates, or at least the TNG/DS9/VOY stardates.