In the immortal words of Lord Ballmer: "Developers! Developers! Developers!" (
Marshall who's been a frequent contributer over at XDA has been working on replacing the default "pie" cursor on Windows Mobile for quite some time now. Up until recently, you had to copy over some system files which made changing your cursor a little bit risky and not something the new user would undertake.
Now with his Marshall WaitCursor2 it could not be easier. Simply install his .cab file to your main memory and launch MWCConfig.
From there you can select from a nice assortment of beautifully rendered wait cursors, including previewing them in action. Then just hit "save" and usually within in a few moments (or after a soft reset) you'll have something nice to gander at while Opera or Skyfire load ;-)
Best of all, this app is free but we here at WMExperts strongly recommend a donation to this fellow as now only does this app works but it is quite aesthetically pleasing (I mean who doesn't want a jumping penguin on their phone?)
Comments from the Peanut Gallery about Windows Mobile even needing a wait cursor will be tolerated, but we'll note that at least when WM experiences inexplicable delays and hang-ups it at least has the courtesy to let you know it's working on something.