Shaikh Ubaid (may Allaah preserve him) says:

Indeed, the scholars disparaged men with what they deserved of disparagement and they (i.e. those disparaged) were not narrators of (hadeeth). And from that (was the disparagement against) Jahm Ibn Safwaan, Amr Al-Jaahiz and many other than them. Refer back to Siyar A’laam An-Nubulaa and other than it among the books of Jarh Wat-Taweel (and) you will know that this (claim that Jarh Wat-Tadeel is specified to the narrators of hadeeth) is a deception among the deceptions of Iblees-from the deceptions of shaytaan. [slightly paraphrased..see link: http://www.sahab.net/forums/index.php?showtopic=147003 ]