Do not buy this mouse to use on Vista! It is not supported with all its features on Vista. The "MouseWorks" software has not been ported to Vista, and the Vista drivers do not support all the features you may be expecting from use of the (formerly excellent) Kensington trackballs on prior MS Windows versions. There is a workaround (download the MouseWorks software, set the properties to "run as administrator" and "run in XP SP2 compatibility mode", and then run) - use a search engine to find more detailed instructions (e.g. http://blog.jeffhandley.com/archive/2007/12/18/kensington-expert-mouse-on-vista.aspx look for Derek Williams' explanation). This workaround is simpler and better than the one using the MS IntelliMouse driver, but doesn't work perfectly either.

One other issue: the scroll wheel feels terrible. The movement doesn't feel smooth, the wheel feels like it is fragile and will soon break, and there is no way to click the scroll wheel for the smooth scrolling you get with a scroll-wheel mouse.

In short, I love trackball mice, and I hope that one will be made that works great on Vista - if one is made, I'll be there to buy it!

I've had the Kensington Expert Mouse Optical USB Trackball for about three weeks now.

General Audience Impressions:

The Trackball is of excellent quality; I've had no problems with it. The wrist pad is comfortable. The scroll wheel makes it worth the price. The key mapping works.

Left Hander Impressions:

As you know most of the trackballs are designed for righties. This one only has one quirk for us southpaws...

I use my index finger to move the trackball and work the scroll wheel with my middle finger. This method for us lefties has the scroll wheel moving in the opposite direction from what I would have preferred - pushing the scroll wheel forward moves to the top of the screen; backward towards the bottom. I haven't checked to see if the wheel direction is configurable, but as is it is a minor annoyance.

Take all the good reviews about this product, and I agree with all the positives. I even like the Kensington Expert Trackball Mouse BETTER than my Microsoft Trackball Explorer (SHAMEFULLY discontinued by Microsoft) in some respects! But I have to admit that my Explorer mouse is a bit more comfortable for long periods of constant use.

I don't think the product description on Amazon mentions that you can assign SIX different functions at a time to this mouse! That's because not only can you assign a different function to each button (there are 4 buttons), but you can ALSO assign a function that works when you press both top buttons together, and another function that works when you press both bottom buttons together! I chose to assign "click", "right click", "cut", & "paste" to the single buttons, and chose "back" and "forward" for the simultaneous buttons. And just in case you don't want any or all of the buttons to do anything when they are pushed, you can assign them to "do nothing" as well. This might be useful for people who keep accidentally pushing a button because of their particular hand shape or hand position.

I've also found that the "fluid" vs. "space down" motion of the scroll wheel depends on the application that is running, and not a big deal to me. If you always want a fluid scrolling motion you can always choose one of your buttons to "drag" the screen fluidly up or down using the trackball.

I mostly decided to write this review to let all you Mac OS X w/ Intel chip and Leopard OS users know that you can get ALL the buttons programmed after downloading "Kensington MouseWorks® for Mac OS X Version 3.0" software from the Kensington website [...]. Never mind that it says it was last updated on 5/30/06 - once you download that version to your Intel Mac (do not click on "search for latest update" when the box comes up so you only download THAT particular version) you can then program ALL the buttons (I own a new 2008 MacBook Pro and it worked for me). At least we can use the available Version 3.0 until they create a newer updated Mouseworks Software Version that fixes the Intel Mac problem.

I LOVE the "keystrokes" option to add custom button settings (i.e. if you want a button to be "Back", first type the Apple "Command" button followed by the "[" key in the top box, and then label it "Back" in the bottom box; I've found that you must label/name it last so that the "OK" button lights up and you can click on it. Likewise, if you wanted another button to be "Paste", choose the "Keystrokes" option, then type the Apple "Command" button followed by "V" in the top box, and then label it "Paste" below and "OK" (save) it. It's so easy to assign practically anything to a button (even opening up an assigned URL or application)...very cool.

And if you aren't able to set some of the parameters for how the trackball mouse responds through the "Mouseworks" application settings, try tweaking the standard mouse application settings.

To think I almost returned this product! Thank goodness for internet searches!

I loved using this trackball under XP, but there are no Vista drivers. That means you can't map/assign the buttons. That's a BIG reason people buy this trackball.

Calling Kensington just gets a non-English-as-a-first-language speaking person telling you they are not going to release drivers for it and to use Vista's built-in support. It's a big show-stopper for me.

I'll have to look for another trackball and forget Kensington in the future.

If you have a Mac or XP, you'll love it. If you have Vista, you'll be very disappointed. I am.

First of all trackballs are not built for gamers. That's being said, Kensington Expert Mouse is an excellent pointing device. Unlike most traditional trackballs this one has an integrated scroll ring and 4 fully programmable buttons. It also comes with a fully transferable five-year warranty. Compatible with MS Windows & Mac running OS X. The only thing I don't like about it is its price. I highly recommend this product.