Having been a long-time reader of Take Control books (and TidBits) I expect to get Yosemite one as well before I upgrade, but it would be interesting to know beforehand what areas a Mavericks user should pay particular attention to, or where problems are most likely to crop up. I'd also be curious what you consider the biggest benefits of Yosemite.
The upgrade from Mavericks to Yosemite is a pretty easy one—much more painless than going from, say, Snow Leopard. Of course you'll want to do a full backup (a bootable clone) before you upgrade, and as always, I recommend upgrading third-party apps before OS X. If you do those two things, the likelihood of problems is small, and they can all be repaired easily :-).
As for the benefits, the numerous ways Yosemite integrates with iOS 8 are quite interesting and useful. I like Mail Drop (when it works <cough>) and I'm prepared to like iCloud Drive (once the infrastructure and third-party support have improved). Extensions will be big, too—again, once third-party support ramps up. And the new Spotlight is almost (not quite!) enough to make me give up LaunchBar. It's really slick.
Upgrading MacBook Pro from Mavericks to Yosemite was not so interesting initially but now, I like a lot to work with this version. Enriched Address bar in Safari browser made many of my tasks very easy and simple. Additionally, other features like keeping single window as Private and managing RSS feeds are also very beneficial.
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