During a briefing today, Nintendo president Satoru Iwata said that Super Smash Bros. for Wii U will feature pre-loading when it releases later this year.
It will allow consumers who have pre-purchased the game to download most of the game's content in advance. This will allow users to not have to wait long for the download after the game's release. After a download of a requisite minimum amount of update date, the consumer can then start playing.
The pre-loading will be available by either purchasing it online or through retailers with download cards. You'll then enter the download code at the Nintendo e-Shop in advance.
Pre-loading is also planned to be implemented on the 3DS next year.