Pros Increased speed
Extended battery life
Great features for improved productivity
Cons I haven't found anything I don't like about the system yet.
Summary I upgraded my mid 2007 15" MacBook Pro 2.2 Ghz intel core two duo to Mavericks from 10.6.8. The most noticeable difference is the speed. My biggest concern when I was deciding on whether or not to update was if my computer could handle it because of its age and it blew me away. The second most noticeable difference is the features. I can now do all the multi-touch movements with my old track pad (the one with the physical button), receive notifications for emails, calandra events and social media in the upper right side of the screen. The third was the extended life of the battery. My old battery would normally last about an hour and this improved it by at least two times. Apple shot themselves in the foot because I was going to buy a new MacBook Pro with retina display in January or February and now I think I'm going to wait another year and make that decision in 2015. Mavericks is the system I've been waiting for.
Pros Everything works faster, and battery lasts longer.
Cons Had to re-enter my Google calendar info to sync to iCal.
Summary Great performance enhancements in terms of speed, responsiveness, and battery life. And can't beat the price!
"Superb for FREE"on by isahiljain
Cons Can't add custom colours to tags
Pros Easy download. I went from Mountain Lion to Mavericks.
Safari is zippier. Like the extra features in Notifications.
Not a steep learning curve.
Cons None so far.
Pros Improved performance
Noticeable difference in amount of RAM used
New apps here and there
Small font, transition and icon changes
Cons Nothing extraordinary
Summary For a free update it's definitely worth it.