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.
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.