Nintendo and Netflix have been promising to give Wii users the ability to stream movies - albeit only in SD, not HD resolution - since October last year, and it looks like it's finally being rolled out. Rather than a firmware update for the console itself, Netflix are shipping out DVDs that enable the functionality on the Wii; according to Dave Zatz Netflix have confirmed that those DVDs are en-route.
The Wii software won't allow for catalog access directly from the console UI itself, so Netflix subscribers will have to load up their Instant Queue with titles from their PC. They'll then be able to choose from that list on the Wii. If you haven't signed up for a DVD yet but are a Netflix subscriber and have a Wii, you can register your details here; the disc and delivery are both free.