Is OpenOffice for Mac OS X ready for use? I am helping a friend set up a brand-new MacBook. She is migrating from a Windows environment and is used to OpenOffice. I have very little OS X experience.

OpenOffice 3.3 has a native Aqua port for OS X > 10.3.

Is this port regarded stable and ready for end users? Is it fully integrated into the OS X environment like Apple's own iWork, or are there shortcomings or compromises one needs to be aware of?
I used Open Office, it does the job ok. No crashes, quite feature complete. However if you really don't want to pay anything for an office suite, I'd go for Google Docs. 

If you do want to pay, then definitely go for iWork. It's the only one that's fully integrated with OS X (especially if you have Lion).