i have two questions i want to ask as i am working on a premium theme.
1. Is it good thing to integrate custom post types in theme (like portfolio). because if someone changes theme data will be lost(correct me if i am wrong)
2. I want display some details above breadcrumbs an striking theme http://kaptinlin.com/themes/striking/blog/ how can i do that (maybe custom field or any other better option)
1. Yes, custom post types are a good thing in general. You’re right that it can be an issue if a user switches themes (the data won’t be lost but it’ll become inaccessible in all likelihood), but that’s just a fact of using advanced WP themes. It does mean, that to the extent you can, storing and cataloging content in standard ways will help the user if they ever decide to switch. For example, you would want to analyze whether certain functionality might be best implemented via Custom Post Type or via Post Format; because Post Format is standardized, if your piece of functionality makes sense to implement that way it can help your users out down the road (see http://markjaquith.wordpress.com/2010/11/12/post-formats-vs-custom-post-types/ for more details on making this determination).
2. That depends on the “details” you want to display, but in general custom fields are a good way of gathering post-specific data. For usability, make your custom fields into meta boxes.
Good luck with your theme development!