It can be difficult to use (webpage) sliders that cover a large range with fine granularity. On the one hand, it is easy to move across the range. On the other hand, it is difficult to locate the exact point one wants, assuming a fine enough granularity.
I was thinking that a magnify effect around the cursor could solve this problem (assuming the problem really exists).
I looked for existing solutions or ideas via google, but couldn't find anything.
Any suggestions here?
I doubt if this is what you're looking for, but... within Mac OSX, holding down the control key and moving the scroll wheel will zoom in and out.
I'm having trouble thinking of a scenario where having so much data that scrolling of this nature would be a problem you'd want to have. In almost all scenarios it makes more sense to chunk up the data or reduce it down in some other way.
About the only thing that makes sense is the seek-bar/scrubber on a video player. If your player is 400px wide with a 360px wide scrubber, but the video is an hour long, the best granularity you'll get is 10 seconds-per-step (with the step-size being 1 pixel).
If that isn't enough granularity, then it's possible you'll need to augment your scrubber with another UI convention - which could be a magnifier - but it could also be other things. Like a "jump to point" text field that would allow to user to entire a time and seek to that exact position.
It sounds like you're going for something (visually) like the OS X dock. This is called a fish-eye effect. There's a jQuery plugin for a fish eye menu which you may be able adapt and merge with a slider to give you the functionality that you're looking for.