The function of the Sony UMD is to hold storage for PSP games, although it seems it come equipped with feature that make future uses possible;
The first possible future function would be; Protective Shutter: Similar to the Minidisc and 3 1/2″ floppy disc, this protective shutter will shield the inner disc from accidental contact. If these discs are ever produced, they will still be compatible with some legacy UMD devices, including the PSP-1000 series. However, they would not be compatible with the PSP-2000 series.
Second possible function would be Auto Loading. These would be similar to the auto loading discs found in car decks.
The UMD has had its share of criticisms. Many feel that due to the limited capacity of the UMD would mean, for instance, that bonus content from movies would have to be removed before it could be released for the UMD. In light of the fact that there are cheaper DVD players that have the capacity to handle bonus content, many questioned the feasibility of the UMD.
Sales have been markedly slower than anticipated by Sony. Complaints began to surface about the cracking of the protective case protecting the disc. A third party company developed replacement cases so PSP UMD users could go on protecting their investment.
There is quite an impressive list of movies and television shows released for use in the UMD. These titles include (but are certainly not a definitive list);
Sony Pictures, 13 going on 30
Sony Pictures, 2 Fast 2 Furious
Troublemaker Studios: Adventures of Shark boy and Lava girl in 3D
20th Century Fox; Alien and Alien vs. Predator
Sony Pictures; Bad Boys
20th Century Fox; Behind Enemy Lines
Sony: Casualties of War
20th Century Fox: Cheaper by the Dozen
Eagle Rock Entertainment: Classic Rock Queen
Sony Pictures: Crossover
Anchor Bay Entertainment; Dead and Beautiful
20th Century Fox; Die Hard, Die Hard 2
MGM: Escape from New York
20th Century Fox; Family Guy, the Freakin Sweet Collection/Vol 1/Vol2/ and Stewie Griffin, the untold story.
Buena Vista: Glory Road
Sony: The Grudge
Sony: The Hallow Man
20th Century Fox; Independence Day
The usefulness and popularity of the UMD remains in question. At one point, sales were so slow that stores started offering B1G1 deals. Buy one, Get one free. Hardly what Sony had anticipated on its launch of the UMD. The UMD has come down in price compared to its release price, which was higher than standard DVD players. This has helped make the UMD a bit more attractive to buyers. There have been no recent announcements concerning the Sony UMD.