We have stayed at Kalypso Hotel for 6 nights and it was a great deal for the money we've spent... it's a small quiet family hotel, on the main road right by the sea. In the morning from our balcony we could see the sunrise. The room was very nice and also the bathroom, quite big and clean.
If you are looking for a place to relax and spend quiet days then you should pick Kalypso. I should mention that our stay was in september, from 18.09-24.09.2011 and there a number of places in Poros that were closed or closing down... I understood from the locals that the season lasts until the first week of september.
We've had a lovely stay and will return again in Kefalonia, it's a beautiful island, waiting to be explored.