Coming someday, alas, only for Mac OS X 10.5+ Universal (Intel32/Intel64). Sorry, few remaining PowerPC users.
A. Essentially, they're a stanndardised syntax for advanced pattern matching. You'll find regular expressions available in most scripting languages and many tools.
It's well worth learning how to use them.
A. This one is largely feature complete and in maintenance mode.
Essentially this means occasional releases to spruce up its look and feel from time to time, and occasional bug fixes to account for platform updates and changes.