Hi BosunCat!
I was on the same trip, genrally I wasnt bothered, but there were varying degrees of 'inclusiveness' from people who had travelled together. Overall, I thought that people who pre-knew each other were fine and did not feel a problem in mixing, I felt more 'resistance' from groups that had formed a clique straightaway on meeting!
I'm VERY independent and in the daytime, on trips/tours for the most part just like being on my own to go where I want when I want. I'm a wanderer and don't like being tied to someone else's agenda/needs, I like to wander around places on my own (although I did enjoy your company in Pisa Bosuncat!), doing things on a whim. The way I see it, it's my holiday and I shouldn't feel obliged to stay with anyone in the daytime, and restrict what I have planned or not planned to do.
In the evening it is different and I did feel some resistance from people who had formed 'cliques' on meeting each other on the holiday, who then went everywhere toether. It's that 'herding' mentality, safer to stay in the herd! But, there were others on the trip who came togther who were very friendly and I felt no barriers at all from them, they included me in everything, whenever I wanted to be included!
Like others have said, generally men don't form 'cliques' like women do and that was true on the Tuscany tour, I personally tried to meet someone different on most days/nights, and not automatically gravitate to the other men on the tour, but there were problems on having to sit at the same table for dinner where you ended up for breakfast, it caused some arguments amongst people! I found it irratating. I noticed that some of the cliques would ensure that they sat at the same seats on ther same table every day, putting up an invisible 'barrier' to others.
Having said all that, generally everybody on the tour were nice and I had a great time. However, I would prefer it if more people were genuine 'singles' so you get to meet more people and you feel less awkward about approaching people. The whole point of Just Ypu for me is that everyone is on the same level, single and out to meet other people and share experiences, without the feeling of 'intruding' into a group or couple.