Let me take these one at a time.
In terms of needing to search again on the site - this will vary from site to site. For sites that have static URLs for the records, we will link directly to that page. These three collections have URLs that are not distinct so there is no way to link directly to the record.
In terms of the experience: I think it is great if people decide to search directly on the web site. We don't want to replace these sites. We want to help people find these websites and know if there are records there about their ancestors. So, the biggest help for this to users will be when they don't know if the content or website exists, they see a result in search results, and then go visit the site.
In terms of crawling permissions, we follow the same web standards that Google, Bing, Yahoo, and others follow. We check the website to see if it allows crawling. If it does and it has useful genealogy content, we crawl it to make it searchable. We have also made it very easy for publishers to contact us and opt out or be removed from the search.
In order to figure out if we were doing it in a way that was respectful to publishers, we talked to a number of publishers and societies to get their input. We also launched an alpha test version of this last fall and announced it on the blog to let people know about it and to ask for their feedback. The current implementation is a result of the input we received over the last number of months.
In terms of data left behind, we are indexing the information most needed to find it and see if it is your ancestor. Some websites have a lot of additional information, some have less. In the case of Allen County Public library, the book and page number are not in our index. Some of the sites will have a lot of data, photos, etc. that will not be in our index.
In terms of value add for a website, we have heard from a quite a few publishers who are very excited to get broader exposure to their sites and content. We know not everyone will feel the same way but the response in our email box has been very positive with dozens of email asking that their website be included in the search.
In terms of the extra page as you go to the website - since this will be a new experience to people who have used Ancestry for a while, we wanted to let them know a little about the experience. One of the things we are telling them is that they may be required to search again. I would expect most people who use this very much to turn that page off - but it will be up to them. Once it is turned off, it is one click to get from a search result to the website.
I hope that answers your questions.