Hamza Yusuf is amongst the `aqlaaniyyah (rationalists), mu`attilah (deniers of Allaah's Attributes), and mutasawwifah - and his collections of video lectures, audio lectures, and his own website (still operative and available online) is ample testimony to this.
The courses taught at his institute use the book "Jawharat ut-Tawheed" - the book that preaches and invites to the heresies of ta'teel and (false) ta'weel and tafweed, a book which is a base and pole for the Mu`attilah.
His institute teaches al-Burdah of al-Busayree which is a poem that invites to Shirk with Allaah, invites to Istigaathah from other than Allaah, and which has been refuted by the Scholars of Tawheed and the Sunnah.
See the screenshot (taken from his website today) attached for a mention of these books used for his curriculum.
You can see some refutations of excerpts from al-Burdah here:
http://www.sahab.net/sahab/showthread.php?s=&threadid=294580
And I have also heard this person on a video lecture making the following two remarks, "This concern with `aqeedah is a sickness in the minds of the Muslims", and "I can go to the desert in Mauritania and learn Tawheed in five minutes", which gives further insight into his ignorance and misguidance.
There is much much more from his lectures, but to be honest, once you hear a few statements like this, and you realise what he is actively promoting, and you are someone who knows and understands the Salafee `aqeedah, you wouldn't want to waste any more time on him or his likes because the affair would be sufficiently clear already. My advice is to study and learn the Salafee `aqeedah using whatever is accessible to you from the speech and works of the Scholars of the Sunnah, and the prominent books such as al-Waasitiyyah, and at-Tadmuriyyah and Kitaab ut-Tawheed so you have a good grounding in these most important subjects.
