WordPress 3.0 was tested by a few hundred volunteers over the course of several months. Most of the current problems are related to plugins which use functions that were warned of being deprecated back in 2.9. Some of these plugins are being updated for WP 3.0 compatibility, and some have been abandoned, so you may need to find an alternative.
Feel free to review the 3.0 known issues here:
http://ww.wp.xz.cn/support/topic/411649
If you consider upgrading, backup your files and database first, then try the automated upgrader.
Of course on here you will notice a number of threads about problems. Most people only come here when they have trouble. You only see the trouble on here, not the success.
I have installed 3.0 using auto upgrade on my 6 sites without a hiccup. I love the new menu system, the new user changeable background feature, custom post types, etc.
If your theme supports these things great, if not, it really should still work. Maybe your theme will be upgraded for 3.0, maybe not…. I edited my own in a few minutes to take advantage of many new features by looking at the new default twentyten theme
Back up your files and upgrade! There’s probably over a 99% chance you won’t need to use your back up at all but it’ll give you peace of mind.
I’d also say yes it’s ready. I was using it in production during both Alpha and Beta stages with no issues. As everyone said backup your stuff and upgrade.
