I reluctantly spent $40 for VueScan after trying unsuccessfully to fix the Canon TWAIN driver which broke after upgrading to OS 10.5.3. After using VueScan for about a month, I'll never go back to using the TWAIN interface (which is still broken anyway). VueScan is so much faster and has so many more options for customization and automation that overall I save a lot of time even if I have to save the scans and import them into other apps. Another plus is that it does a better job of cleaning up scanned 35mm slides and restoring the correct color of faded ones. I also really like the ability to save Profiles of settings for different tasks.

My only quibble is with the documentation. The User Guide accessible from VueScan Help is an HTML document with no search function. Fortunately, there is a .pdf version downloadable from the developers web site.