Francisco accomodated 25 of us on a recent visit to Lisbon (May 2013), at the Palacio do Ramalhete.
He was very helpful in advance arranging the day, and flexible in terms of food/drink/costs etc. to accomodate our needs.
The venue itself was unbelievable - a really great place to spend the day. We originally planned to spend a couple of hours at the wine tasting and move on, but ended up staying there for the afternoon!
I highly recommend this experience if you are visiting Lisbon and looking for something to do as a group.
If you own or manage Venha Vinho, register now for free tools to enhance your listing, attract new reviews, and respond to reviewers.