depends on what kind of rehearsal dinner it is. for a wedding i would think it's too casual. i LOVE free people! i wish their sales in the stores would be more consistent with the online sales. sometimes its priced less and sometimes its more. i never know what kind of a deal i will be getting.
I love free people, but most of their clothing is hit or miss.
the tube top you picked out is really cute, its a little casual to me but you can easily make it formal with what you put on bottom. What scares me is that the title of the shirt is graphic tube, which doesnt sound formal.