Yes - I have the same problem with GIANT TEXT on my Bold 9650 after an official upgrade to OS 6.0. Really frustrating and nothing about it on the Viigo forums. I miss my Viigo but unfortunately I've started looking for other RSS readers.
You can use the Alt key and trackpad zoom to make it smaller, just like in the browser. It goes back to large when you go to another page, but it allows you to use Viigo untill they come up with an update for 6.0.