Many Sefardim still accept Yibum today, per the Beis Yosef in Shulchan Aruch, EH 165:1. See MDG above for that and other sources.
Joe:
100% correct. There is a Machlokes Rishonim as per who we Pasken like. Ashkinazim hold like Abba Shaul, and Sephardim hold like the Chachamim.
In fact, HaGaon Rav Yosef Shlita was insistent (IIRC) in allowing Yibbum for Sephardim, even while the Ashkinazic Rabbonim in Eretz Yisroel were trying to disallow it for everyone.