Go ahead and install FileMaker Pro 10 on your Mac. There is no need to uninstall FileMaker Pro 8 if you don't want to.
When you have FileMaker Pro 10 installed, open a FileMaker Pro file and see if it launches with v10. It should.
If not, Get Info on the file and set the "Open With:" to FileMaker Pro 10. Then click the Change All... button. That should do it.
Version 10 features will be available in all your files. No conversion necessary.
David - Thank you for quick reply. I bought FileMaker Pro 10 and installed it w/o uninstalling 8. My database opened in 8 so I changed it on Get Info. Then it would not open but said it needed to be Recovered. I did that - said it had 61 bad blocks - then it said all was well ... and it appears to be so. I am going to start entering and see if anything goes wrong. Hope not. I will only write again if there are problems. Thank you for the help.
The consistency check has been beefed up in FileMaker Pro 10. The bad blocks found may be the source of your 'erratic behaviour' in FileMaker Pro 8. Hopefully all will be well now. And you are up to date!