I think it is better to say: " what is new about Sarah?" or simply: " how is Sarah?" " Do you know anything new about Sarah?" ;)

'what's up with 'x'" usually means there is a problem or a concern. For example, if I cant access CNN I might say 'What's up with CNN?' meaning 'what is the problem with receiving CNN?'. It isn't a greeting, it is an indicator of an unknown with the subject in question. I guess you could say it means something like, 'what is the problem with...'

Maria you can also say that hat About Sara .. ok many sentense you can use but i use "What's About sara" .. am i rite @language fan ?????

Thank you honey. I like it. It's kinda artistic :)

Yes, you can. Actually, "What's up with Sara?" might imply that there's been a problem involving Sara recently. However, amongst good friends, the phrase can be used quite loosely to ask about someone's well being.