Actually, +1 has been available for a while on search results, but you have to sign up through Google labs to see it.
Tomorrow's announcement is said to be the launch of +1 for websites. Sites will be able to place a +1 button on their pages. Then when people are doing a Google search, there will be an indication of whether your contacts have +1'd a particular listing, as well as how many people have in total.
So imagine that the number 1 result in the SERPs for a particular keyword has 20 +1's while the number 3 result has 500 +1's. Suddenly the number 1 spot alone is not nearly as attractive.
+1 will also appear next to ads. Again, the implications of this are huge.
And obviously, the potential for abuse is just as large.
It seems to me that this will be a huge shake-up for both the SEO and the PPC worlds. Am I missing something?