See: http://forums.slimdevices.com/showthread.php?t=49086

Quoting:

Is there an easy way for the web UI to change the mouse cursor into an hour glass or other "wait" symbol when items are being added to the currently playing playlist?

I'm in the habit of adding whole cds at a time to the playlist. With the new JS code under the hood, it seems as though sometimes my clicks don't "register." It feels like timing is important here: hover just a little too long over an item before clicking the [+] control and the click goes unnoticed by the UI. Currently, the only visual clue that a click has resulted in the desired action (on long playlists where the bottom is below the browser's window bottom) is if the playlist pane scrollbar control gets smaller.

A switch to the "pointer plus hour glass" cursor [the "working in the background" cursor] while the items are getting tacked onto the bottom of the playlist would provide a helpful visual cue.

Some JS that may do the trick:

http://www.hscripts.com/scripts/JavaScript/mousecursor-change.php