I read that we can store list items limitation for sharepoint 2010 is 30 million . Is this true ?
If yes , then can i have 25 million records in sharepoint list , and use "export to excel sheet" and it will work fine ?
Yes this is true, as per technet.
Items 30,000,000 per list Supported You can create very large lists using standard views, site hierarchies, and metadata navigation. This value may vary depending on the number of columns in the list and the usage of the list.
But milage vary as in the description mentioned that its depend how many columns of different type.
I dont have a list this much items, so only way to check is test it.
I dont think so it's good idea to have list with 25Million items, this will be big performance hit on your site.