im seeing some mixed opinions here.
some saying no, some saying yes. So truthfully it all a matter of WHAT features you think you need.
IMO I'd get it if I were you, $69 is a fantastic price expecially if you to compare or imagine it was Vista you'd upgrading to. I know that sounds dumb but what I mean is Vista is $120 for the most basic version. Meanwhile Leopard is the ultimate version no matter what. (I think Vista ultimate is nearly 500 bucks) But anyways enough on why that price is great.
Leopard has alot of features that I cant imagine living without, suhc as Quickview. EASILY the most useful feature ever. I know OS X Tiger shows previews of basic images sucvh as Jpegs. BUT leopard shows previews of nearly any format. Its extremely handy, plus idk why it makes the computer look and feel alot fancier. IDK why just the feeling of clicking on a .avi file on your desktop then pressing simply space bar, and that file appears to enlarge into a transparent window and ebgins playing the video instantly just feels really 21'st century and fancy.
Some may argue that Leopard is alot slower then Tiger, but honestly I dont notice a difference on my 2.0Ghz C2D macbook with only 1GB of RAM, and yoyur iMac is WAY more powerful then my macbook and manages to run Leopard absolutely fine. Speed should be the last of your worries.
Leopard also includes lots of subtle improvements, and nice features that I cant determine how much you'll use. But i can garuntee that if you enjoy Tiger, you'll enjoy Leopard JUST as muhc if not more.
About all those "issues" you hear about, that is simply because it is MORE common for someone to come on here and complain about something, then it is for someone to come on here and praise leopard. What i mean is the people who love leopard generally stay quiet and simply enjoy it to themselves. but the people who hate leopard (for whatever silly reason) will raise their voices and make sure they are heard. Trust me leopard isnt as buggy or issue filled as these forums might make it seem. Also any issues you DO have, people such as I (and hundreds of others on here) will happily help you out.