On the official Saints Row forums, a moderator has confirmed that there will definetly be a PC version of Saints Row 2 and that it will be released on the 6th January next year. They have explained the delay is due to the fact that they wanted to get the quality of the final release right, although it will be a port of the console version they are working on features only available on a PC, such as adjustable quality settings, multiplayer server features, using a keyboard and mouse, as well as being able to map your own keys as you see fit. Volition have admitted that it will be an external company undertaking the port, but they are working closely with the company to ensure "PC users [have] the same quality product and performance level which you've seen on Xbox 360 and PlayStation 3". Minimum and recommended system requirements are still yet to be announced but the Volition moderator has said they will be updating the thread as soon as they are allowed.
You can find the Saints Row forum thread here.