FLEX: how can I get the width of my linkButton object ?

First, what does that trace() show? Is it null or undefined or NaN or simply a wrong value?

Then, there are several ways I can think of how you could get around this problem:

Try using getBounds() or getRect(). These methods return a Rectangle object working as the DisplayObject's bounding box (including all coordinates and dimensions). Sometimes Flex behaves a bit weird and returns wrong/off results for the coordinates or dimensions of objects.
Try experimenting with validateSize() and/or measuredWidth. Perhaps you're trying to access the width property too soon so that Flex cannot do the measuring/layouting in time.
Similar idea: what happens if you use myContainer.callLater(trace, [myContainer.width]); (assuming your myContainer inherits from UIComponent)? If you do get a valid result using callLater() but not when accessing width directly then Flex just hasn't had a chance to layout and update the container.
You could also try using this method, which creates a Bitmap from the object and returns the Bitmap's height/width. This is especially useful if you have components with visible = false in your container, because Flex doesn't handle invisible components well in that regard.
Finally, you could try accessing $width in the mx_internal namespace and check that property's value. However, using mx_internal is sort of a very ugly hack because these properties and methods weren't meant for external use and are subject to change any time (so your component could stop working when a new version is released) - so use with caution.

ansaurus