I can view a user's submitted answers, and the accepted ones are colored differently. But is there any place that summarizes how many have been accepted? If a user has say 1000 submitted answers, how can I find out what percentage of them have been accepted?
To get the answers that have been accepted that a particular user has given try something like this query. You can adjust the user number to check another user.
In addition to search, you can use the Stack Exchange Data Explorer, although the data there is only updated on a weekly basis. (Mind you, for users with a large number of answers, I wouldn't expect their accepted answer percentage to undergo dramatic changes from week to week.)
This query will just tell you what percentage of a user's answers have been accepted, just give it the User ID of the user you are interested in. (I'm currently standing at about 58.8%, in case you were wondering.)
This query will give you the top 100 users by accepted answer percentage among those who have posted some minimum number of answers (given by you as input). (Currently, the top user by accepted answer percentage among those with at least 1000 answers is Daniel Fischer. No relation. That I'm aware of.)