Looks like Taylor Swift is on a roll with guest artists. Tuesday night at her show in Los Angeles,  Swift had Justin Bieber onstage for "Baby".  On Wednesday night, Jason Mraz joined Taylor to duet with her on his song, "I'm Yours."   Taylor tweeted, "I couldn't love LA crowds more. I can't believe how awesome tonight was. And thank you Jason Mraz for singing I'm Yours with me!!"    Taylor has two more shows to go at L.A.'s Staples Center  Saturday and  on Sunday. I wonder how she is going to top these 2 guests?