API Notes

Current Trait/Type organization

(this uses "C" for structs and "I" for traits)

A few things to note:

There is no such thing as Time, only NaiveTime
Date<Tz> doesn't actually make sense.
TimeZone has an associated Offset type which is always a TimeZone which implements Offset and except for Local is always the same type as the trait is implemented for. (That is Utc::Offset is Utc, FixedOffset::Offset is FixedOffset, but Local::Offset is FixedOffset).
Almost all of the constructors for DateTime are on TimeZone, although you can get to a DateTime by way of NaiveDateTime::...::with_timezone, which is a really ugly API, but one that people keep re-inventing.

Construction of DTs is confusing
Large number of types/traits that are not necessarily named after what they do (mostly just that constructors are in TimeZone)
Local is kind of just another FixedOffset
- Except that FixedOffset doesn't have a way to load the current time, just Utc.now() and Local.now(). I'd rather get rid of Local in favor of FixedOffset::local_offset() or something less ugly (chrono::now_local() vs chrono::now_utc()?)
Bad error messages for parsing/unparsing
No types for time units (enum Month, etc YearMonth is obvious), this is necessary for nice iteration (current implementation in PR from gnzlbg) and maybe constructors
Obvious methods panic internally, must use *_opt() methods to get Options (not results)

definitely more

At least think about converting to other calendar systems
No-std support
Iterators a PR exists, but I would like to make sure that all our iterators have an intuitive API.