StumbleUpon Toolbar
One of the internet tools that I use most is the StumbleUpon toolbar. It is how I have come across 90% of the internet tools that I know of.
It is an easy-to-use but very powerful and useful social-bookmarking and website discovery tool.
Being very useful, it allows you to literally “Stumble Upon” tons of websites related to categories and topics you want to see. It’s very fun to use and leads you to great sites - regardless of what you are looking for 
The Toolbar:
You first have to choose categories and topics you are interested in and that you would like to browse. You do this in your profile.
Once you have done that, you simply choose what category you want to browse from the toolbar and then Stumble away!
As you are Stumbling, you can rate pages with a simple “Thumbs Up” or “Thumbs Down” (see above Toolbar Image).
Every page that you give a Thumbs Up is saved in your SU (StumbleUpon) community profile and you can view them later. Other community members can see them as well to get to know you better.
This leads me to add that SU has a strong community “side” to it. You can search or browse members and filter results down to specifics such as Gender, Sexuality, Location, Interests, etc. You can easily make friends on SU.
I love how quick and easy StumbleUpon is to use. It’s easy to save pages for later, and makes for quick page stumbling/browsing.
I can’t conjure up any things I would change to SU. It covers everything I’m looking for in a Social Bookmarking/Website Exploration site.
However, I do think it would be neat if SU would automatically save all “Thumbs Up” sites to a select folder in my Bookmarks.
Links
StumbleUpon has an Online Demo for you to try before you download.
It is available for both Internet Explorer and Mozilla Firefox. Click to Download
The Run-down
StumbleUpon is a great tool if you are looking to explore websites, or meet friends with similar interests. It also is a great Social Bookmarking site.
It’s top features include it’s Community-feeling integration as well as it’s ease of use and enhanced interface.
We give it a rating of 5/5
What do you rate it? 
(6 votes, average: 5 out of 5)
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Once you’re a StumbleUpon User, why don’t you come back and Stumble this Post and this Blog! 
Excellent time with Stumbleupon. However, I am being inundated with Trojans and Spyware!!!
Nice information guy, that’s be useful for me to learn more about Stumble Upon.
Thanks.
So how do I install it on my mac?