Is it advisable to update to latest OS on 6 year old iMac running OS 10.6.8?

If you have at least 4 GB RAM. More is preferable. You won't be able to use any older PPC apps--Rosetta is no longer supported. Not only Rosetta/PPC apps, but some of your apps might not be compatible. See http://roaringapps.com/apps

Best would be to try it out on an external drive first and see how it runs before upgrading. If you do like it, and if you have enough room on your internal hard drive, create a second partition and dual boot both Snow and Yos.

Probably most important reason to upgrade would be that Apple is no longer supporting Snow Leopard for security. Not only the OS itself, but Safari and Mail are vulnerable to exploits.

Help us with a little more information:

• How much RAM is installed (from "About this Mac')?
• What processor (also from "About this Mac")?
• What applications do you use commonly?

The last one is important for two reasons:

1) A computer running Pro apps like Creative Suite, photo and video editing software, and CAD programs need more RAM than one used for simple word processing, spreadsheets, e-mail and browsing. 4GB RAM seems to be the smallest amount of RAM you can use to run Os 10.10 without encountering slowdowns. Early 2009 iMacs (identifier code "iMac9,1) can use up to 8GB RAM; the Late 2008 21.4 inch can use 16GB and the late 2009 27-inch can use 32GB.

2) OS 10.6 still allows you to run older apps like Office 2004, older versions of Creative Suite, etc that were written for pre-Intel Macs. Starting with OS 10.7, the emulator function allowing that was deleted from OSX.

In a way it is a personal choice, however as WZZZ mentioned there are things to consider.An additional item to consider is if you add new devices such as iPhones, iPads. etc they will require more up-to-date versions of OS X. Personally, I have found it less painful to upgrade on a regular basis then waiting many years as the possible cost of upgrading apps in one year is more difficult to burden then spreading it out over many years.

As WZZZ mentioned, 3GB of RAM is adequate but consider getting more. If you do, please ONLY purchase from reputable vendors such as OWC or Crucial, iMacs tend to be fussy when it comes to RAM.