Updating a jquery progressbar via button clicks
Not sure if it is helpful, but since we are on codereview, allow me to give it a shot.


there is a progress element available in HTML5 that works very easily and is fairly well supported (http://caniuse.com/progressmeter), except for in IE off course. I would suggest using this in stead of the (heavy) jquery-ui you use now.  
When writing js code, avoid global variables at all cost. They take up resources, and some day they will come and haunt you when you accidentally overwrite a variable that you forgot about. Keep your variables in function scope whenever possible.
when you see yourself writing the same code more then once, with just a minor difference in one of the values, try to think of a way to reuse your code. It will decrease the number of bytes, make your code better maintainable, and almost certainly improve the quality of your code.  
Be careful with setTimeout. It can be a very useful and powerful tool, but it costs quite some resources. When working with jQuery, try to use their functions in stead. They have been used and tested millions of times, and you are a lot less likely to mess things up when you use them.


With those tips in mind, I tried to rewrite your code.The full version is in the updated fiddle, and the javascript is here:

// changing progressbar when button is clicked
$(".button").click(function () {
    animateProgress(parseInt($(this).data('diff')));
});

// animate progress by a step indicated by diff
function animateProgress(diff) {
    var currValue = $("#progress").val();
    var toValue = currValue + diff;

    toValue = toValue &lt; 0 ? 0 : toValue;
    toValue = toValue &gt; 100 ? 100 : toValue;

    $("#progress").animate({'value': toValue}, 500);
}