Reconfiguring a 2009 iMac

Hi all,

A few years ago I switched from Windows to Mac. I bought myself an iMac, and I'm happy ever since.

Now I want to completely reinstall my iMac because over the years I've tried different kinds of software (paid and freeware) and user-configurations, and now I know what software I really need and how I think I want the different user configurations being set-up. Uninstalling the software I don't use (anymore) does leave a lot of 'garbage' on the computer. That's why I thought that reinstalling everything would give me a clean fresh start.

When I bought my iMac it came preconfigured with Leopard. I updated to Snow Leopard, and this year I switched to Lion.

Question 1:

Do I have to follow this same procedure when reinstalling the OS, or can I just start with the OS X Lion installer I bought (and downloaded) a few months back as a Snow Leopard update/upgrade?

Question 2:

Up until now, I had one account for me with all privileges possible and used this account for all my work, and one account for my girlfriend, with limited privileges, for her work. I'm not sure if it is true but I have always found that my girlfriends' account runs smoother and more responsive then the account I used.

So, I also would like to know (because I've read different scenarios about it) how to setup different user-accounts. Some say you create one account with all privileges possible to administer the iMac, but don't use that for regular daily use. And besides this admin-account you create per person accounts with limited privileges to do your daily work (and install the needed software per account).

Because of my findings with my girlfriends' account, I tend to believe this is a good scenario.

Is this true?

Thanks.