I was in IB for all four years of high school, but chose not to do the diploma candidate because they were requiring beaucoup hours of community service at the time, and I didn't have the spare time to do it between football, basketball, and WORK. 😉 It was unfortunately a bit cliqueish as the majority of the kids in the program were from upper-crust families (the kind where mommy and daddy give you a new Mustang for your 16th birthday) so most of the people I associated with weren't even in the program. Other than the Richie and Rachael Richs of the world, HS was actually pretty much a blast . . .
Anyway, I did well on all of my IB exams (French, english, and history I believe. I seem to remember certificate candidates could only take three tests, but I could be wrong.) I got certificates in all the tests I took, and I presented them to the admissions counselor when I enrolled at Purdue - and she'd never heard of the IB. I'd heard you could at least get some 100-level credits or at least get the option to test out with the IB under your belt, but they wouldn't do it.
Would I do it again? Yeah, because the teachers were some of the best I'd ever had, and the quality of the education was a good start on college - but don't do it expecting to get any real benefit out of it.