The current trending is a nonsense, in fact I'd go so far as to say it's dumb and wrong.
For example, if I'm looking at Monthly Uniques for March 29-31 the trend data is incorrect and misleading given that it is based on 4 weeks prior – which was the start of March. This is because Monthly Uniques is typically higher at the start of a month compared with the end of a month.
My suggestion is that rather than providing a dumb trend, Omniture needs to provide a smart trend based on a much more sophisticated (but still relatively simple) rule.