Is it just us, or does it feel like everyone in Hollywood is celebrating Reese Witherspoon 's 40th birthday? Taylor Swift and Keith Urban performed at her party . Kate Hudson and a slew of other stars turned up. Chelsea Handler took a nude selfie . What more could a gal ask for?Oh, how about spending the actual big day with yet another superstar? Witherspoon shared a photo from yesterday's birthday dinner, and her special guest was none other than Nicole Kidman . The pic shows the Australian actress watching her pal blow out her birthday candles.