Notification Center:
Apple has decided to add the Notification center with all the similar settings with notification display and placement just like it is on the iPhone and iPad.  It is one of my favorite because of how easy it is to simply view all notifications and alerts in one place.
Twitter integration
With Twitter integration you can simply tweet from notification center, right click on objects to send it our via twitter.  Facebook integration is due to come this fall as an update.
Safari unibar
Safari now has the long awaited feature where you can simply search Google via the URL bar just like you could on Google Chrome.  Other updates includes iCloud browsing so that you can continue to browse when you leave your iMac on your iPad or other iOS devices; you can also add pages to reading list and share via Twitter or iMessage and you also have tabbed pages.
Notes + Reminders
Reminders is a rather simple to-do list, but with one impressive feature: you can set alerts to appear when you leave or arrive at a location. Type in ‘Work’ or ‘Home’ and it looks up the location from your personal details in the Contacts app, then ring-fences it.  Notes app now separated from your mail app to be stand alone with same interface as iOS version; it also allows you to sync your notes with your other Apple devices via iCloud.
Dictation
Dictation tool is not turned on by default but going into settings you can switch it on.  It is very useful for dictating notes or any app where you are able to type normally.  It is just about 95% accurate with recognizing speech.
