I’ve been running OS X Mavericks for over a month on my MacBook Pro Retina and while there are a few new bugs, the overall experience has been very good.
Now I have converted over my desktop computer, and that’s more of a risk than a laptop with one drive used for travel and miscellaneous (drivers, printing, etc). But so far it has gone well, the main issues revolving around dual-display behavior which has changed in Mavericks, and is still not well considered or thought out.
I have no real concerns for mainstream users updating immediately, but my advice to most professionals is to defer upgrading for 2-3 months, and let the first batch of bug fixes work themselves through, particularly things like printer drivers and drivers for specialized hardware. There is no rush to upgrade, and if daily workflow depends on specific devices or printers or similar, caution is advised as with any release.
Update Nov 5, 2013: I spoke too soon. Mavericks has all sorts of bugs ranging from annoying to nasty to broken APIs to crashes. It is at least as bad a Core Rot as any release. Wait till 2014 to upgrade—it’s just not worth it.
Virtual memory / compressed memory
Compressed virtual memory is a BIG WIN for users having Macs with not quite enough memory.
So far, casual printing use with a Canon PIXMA Pro-10 is working OK, with the usual caveat of insanely broken multi-dialog print setup, but that has been a confusing mess for years.