That is, I am interested both in views of what formal diagnostic criteria are being used - and how far are they valid? - and to what extent, in the real world of clinical practice, any such formal diagnostic distinction hold good.
The term hysterical is classic and the somatoform disorders (between them somatization disorder) are part of the DSM IV and ICD 10 classifications in an intent to "formalize" hysteria.
Both classifications have tried to divide hysteria between diverse symptoms, however the validity of certain somatoform disorders are in discussion. In theory somatization refers to a number of physical symptoms of diverse systems or organs that cannot be explained clinically or by auxiliary tests. On the other hand conversion refers only to pseudoneurological symptoms, usually, after a situation that cannot be processed mentally by the person.
some how intense and rigid categorization of human behaviour makes it difficult to be treated, after all whether be it DSMIV or ICD10 both are based on human obervations, and it is very likely that may be the classic term may be applied to human behaviour in US but is very hazy in India or Pakistan due to cultural differences or cultural effect on manifestation of human behaviour. So go for a broader view and not for fine differences in man made catagorization of human abnormal behaviours.