New PHP 5 configuration directives:

realpath_cache_size integer
Default: "16K"
Determines the size of the realpath cache to be used by PHP. This value should be increased on systems where PHP opens many files, to reflect the quantity of the file operations performed.

realpath_cache_ttl integer
Default: "120"
Duration of time (in seconds) for which to cache realpath information for a given file or directory. For systems with rarely changing files, consider increasing the value.

date.timezone string (list of valid values).
example: date.timezone="America/Denver"

allow_url_include boolean (same role as allow_url_fopen). The default will be false not clear if this is really part of 5.2. Some documentation indicate this will be avaialbe in PHP6.0.

Some minor (for most) changes to error types.

Some new extensions (some enabled by default).

Official change details.
Official change_log.