For people who have a long history with Macs, it would make a good Mac OS 9 (or 8.6) machine, to run your old programs and games. You can run most Mac OS 9 apps under Classic in Mac OS X (up to Tiger), but some programs (especially games) do not work or work well under Classic. So it's good to have a Mac that boots Mac OS 9 (or 8.6) directly.
If you do any writing or number crunching, it would make an excellent +processor of words and numbers+. Some people find they get more work done if they are not constantly distracted by today's Internet-dependent computers. Microsoft Office 98 and 2001 for Mac are great program suites that work great with Mac OS 8.6. AppleWorks is a great
work suite too. WordPerfect is another great program that is available for free.
http://main.system7today.com/software/wordperfect/wordperfect.html
That web site, System 7 Today, is a great resource BTW. It's focused on System 7.6 and earlier, but a lot of its content applies to 8.6. It might give you some ideas for what you can do with the iMac.