I've been using Ancestry.com, as a guest, lately. Ancestry allows members to make their trees "public", which I would guess means to make visible to anyone who is a registered Ancestry.com user, subscribers or guests.
The good news is that I can search these trees. Beyond that, they're barely usable for guests.
Specifically, I can click on a search result which connects me to something like a family group sheet for the individual search result. This can be helpful, but I am not allowed to view a tree that might allow me to quickly navigate back or forth generations and quickly scan surnames. To see marriages, I can click on a parent or sibling in the family group sheet, which sometimes takes me to a new family group sheet. Mostly, a click takes me to a subscription page and tells me to become a paid member. Whether or not I get sent to the next family group sheet (but never a tree) seemed to be arbitrary, but much more likely to be the subscription page. I doubt that is what members expect when they make their trees "public".
As a family genealogist, I've been given access to family members' dna test results, including some on Ancestry.com. For any of you who have tried to identify "dna relatives", you know how difficult this can be. It helps immensely to explore family trees and search for surnames in common. Although many of the trees are "public", I am not allowed to view any of them, nor the family group sheets sporadically available through the search function. Making it difficult to research dna.
Addendum: I have found that once I establish a research collaboration with an ancestry.com member, that person can "share" their tree with me, which then shows among my "trees" when I login as an ancestry.com registered user. So if you identify a cousin through some other research - in my case a dna match on MyHeritage.com or 23andMe.com - and if that person has a tree on ancestry.com, he/she is able to "share" their tree with you, giving you access.
