Since the subject comes up so often and my fingers are screaming at me that they've typed these words so many times before, here are some things that should help you keep Painter 6, Painter 7, and Painter 8 running more smoothly. They won't answer every possible problem, but they're basic and worth doing in any case.
Painter 6, Painter 7 and Painter 8, with more complex brush variants and multiple Layer types, are particularly processor intensive and use a lot of memory. There are some things you can do to help make it run more smoothly, though.
1. Lower the number of Undo's if you have it set to the maximum of 32:
Edit > Preferences > Undo
2. Lower the number of days Painter auto-saves scripts (the maximum allowed is 10 days):
Edit > Preferences > General
In the Auto Save Scripts for [ ] Days box, type the number you want.
3. Use a smaller Scripts Library:
If you've recorded any scripts you want to save, in the Objects palette's Scripts section menu, choose Script Mover and create a new Scripts Library (click the New button in the bottom right corner of the dialog box and give your new Scripts Library a unique and descriptive name). Then drag those script icons from the currently loaded Scripts Library on the left panel into your new Scripts Library on the right panel.
Then, when Painter is closed, go to the main Painter application folder and delete the default Painter Scripts Library file. In Windows it's the Painter.ssd file. On Mac's, it's the Painter Script Data file.
When Painter 7 is opened again, a new empty scripts file is regenerated and whatever you do in that Painter session is recorded as a new script.
4. Close other programs while working in Painter.
5. Each time you close Painter, go to the appropriate folder for your Painter version and check the size of the Pre-built Brush File. If it's large, delete it. You'll find this file in the following folders:
Painter 6 main application folder
Painter 7 > Brushes folder
Painter 8 > Brushes folder
I delete this file if it's over 1 MB, though your system may be able to handle letting it get larger than that. Testing the Impasto variants one day, the "PBF" grew from its base file size of 113 kb to over 60 MB in less than 20 minutes, so if you're using complex brushes like Impasto, Water Colors, and Liquid Ink (and some others), you may need to check it more frequently. This is also true for some custom brush variant collections available to download from various sites. Chris Cimonetti's Fine Art 2 brush library is a good example. You'll find the Fine Art 2 brush library by going to the PixelAlley Section Links Page (http://www.pixelalley.com/pixelalley-sections-pages.html).
It doesn't hurt anything to delete the Pre-built Brush File as it's used to store brush information and make brush building (by Painter) faster. It's regenerated the next time Painter is opened.
6. Always save your work frequently and no matter what you're doing in Painter, after working for an hour or so, save your file as a Painter RIFF, shut down Painter, and check the Pre-built Brush File size.
7. Use Save As and save your RIFF files in a numbered series. For instance:
8. If you experience corrupted RIFF files, save your files Uncompressed. The default is compressed, so you'll need to check the Uncompressed box when saving.
NOTE Never use Impasto settings with Water Color brushes or Impasto variants. This can cause immediate and permanent corruption of your image, and right before your eyes, to boot!
9. Do regular system maintenance tasks.
In Windows, at least, and I am not a Mac user so can't say what system maintenance would be needed, run ScanDisk and Defrag at least once a week.
Regularly clear out browser cache and temp files, even several times a day depending on how much you're on the Internet, whether you've downloaded files, etc.
10. When you've done all of the above and Painter becomes sluggish, use Save As to save your file as a Painter RIFF, close Painter, delete the Pre-built Brush File if necessary, and reboot.