Visited Casa Grec in January 2010. A wonderful experience in terms of service, food and ambience. I would highly recommend the restaurant for a "special" night out.
Located just off the main Argostoli sqaure, behind the Mirabel Hotel.Sadly Gemini is no more. The doors were closed about 3 years ago and last year it was car parking space!
The Dum Spiros I know is in Svoronata. It is a very good taverna, with plenty of good quality food, excellent service even at the busy times of the season. We have also benefited from their generous hospitality with house compliments home made sweet.....