I host a site at Yahoo and I'm wondering if it will hurt to switch particularly with my Yahoo search results?
Nope, as long as the switch is fast. My suggestion, first transfer all your sites content including databases to the new server and ensure every thing is running and only then change the name servers and ip address.
I've move my sites around several servers and it did not affect the PR ranking at all. As long as your sites are up at all times and that you maintain the domain name, PR should remain assuming all other PR parameters remain the same.