I remember him back in that issue of Avengers #34. The arrogance combined with his powers made him formidable. Avengers and Thunderbolts threw everything at him, and he just keeps coming. Thought it was awesome the way Vision phased into him (which was a twist on their previous encounter):
Other than that though, I'm not too familiar with Count Nefaria's other appearances. Wasn't he supposed to be from one of the Maggia's families? He headed the Maggia? Last I saw him, he was fighting Doc Ock in San Francisco.