The Canon EF 70-300mm f/4-5.6 L IS USM Lens is a great studio portrait lens - especially on a full frame body. It has the best portrait focal lengths, great image quality, image stabilization (helps greatly with accurate subject framing), has very reliable autofocus and does not flare (very helpful when studio lights are aimed toward it). This portrait was obviously taken with studio lighting - here is an overview of the lighting setup:
Just right of the camera, close to the subject and just out of the frame is the main light - an Elinchrom Digital Style 1200 RX Monolight fired into a 53" Elinchrom Rotalux Junior Octa Softbox. Just outside of the frame to the camera left is a 32" White Photoflex LiteDisc mounted to a lightstand. The reflector is bouncing light from the main strobe back into the subject - to fill the shadows.
The rim light is coming from an Elinchrom Digital Style 600 RX Monolight fired into a 20x51" Elinchrom Rotalux Softbox aligned about 180 degrees from the main light. The background is being lit by an Elinchrom Digital Style 600 RX Monolight fired into a 14x35" Elinchrom Rotalux Softbox positioned horizontally just above the floor behind the subject. A background light stand was used to hold this light. The subject is sitting on a simple kitchen stool.
The background is Savage Widetone Seamless Paper in #27 Thunder Gray (neutral color - goes with anything - can be lightened by adding more light from a strobe) held by a Manfrotto Background Support System. The strobes were triggered wirelessly using PocketWizards
The result of all of this is of course the important part - a picture that reflects the beauty of the subject. Soft lighting on the face (no harsh shadows) and nice separation from the not-competing-for-attention background results in a clean, attractive portrait. The 100mm focal length is a good choice for this portrait framing.