Have a BlackBerry and an iPad and want to tether? Bla1ze over at CrackBerry.com found himself in just that situation, and so he put together a quick how-to:
The process requires you to download a cydia app called iBluever and a BlackBerry application called PDANet. After a few setting adjustments you technically should be up and running using your BlackBerry data plan with your WiFi enabled iPad. That said, you should keep in mind that anytime something is interacting with your carrier data, you could incur extra charges. if you decide to set this up, you do so at your own risk.
Have you tried tethering your iPad to your BlackBerry? If so, let us know how it worked for you.