I think it depends on your OS and what software you expect to use to run the scanner.
I use a Canoscan 8400f, and when I upgraded to Photoshop Elements 9 (Intel) from Elements 3 (PPC), I discovered that it no longer used the scanner interface, Twain, by default, but you could install it and use Twain if you wanted to, but it was not recommended. The alternative was to use another scanning program, such as Apple Image Capture, which did not have all the features. Other scanner programs are available that may help.
I reinstalled Twain and found it works fine for me, YMMV. Unfortunately, I can't remember exactly where I figured this out or what I did. I think it was buried in the PSE Help command. It continues to work on my early 2008 MBP and mid 2011 iMac 10.6.7. Haven't tried it under 10.6.8 yet, having just upgraded.