Here is the definition from wikipedia. "Vaporware (in British English: Vapourware) is software or hardware which is announced by a developer well in advance of release, but which then fails to emerge, either with or without a protracted development cycle. The term implies unwarranted optimism, or sometimes even deception; that is, it implies that the announcer knows that product development is in too early a stage to support responsible statements about its completion date, feature set, or even feasibility."
So what's so bad about it? NOTHING! Infect one of the longest-running vaporware project known as project xanadu is one of the basis of the world wide web. Although Tim Berners-Lee is to be credited for the w3 some of the technologies (The hypertext mark-up language) used were results of long running vaporware projects. Example; HyperMedia : is a term used for hypertext which is not constrained to be text (it can include graphics, video and sound). W3 is a wide-area hypermedia information retrieval initiative aiming to give universal access to a large universe of documents. The term hypermedia was coined by Ted Nelson around 1965. Project Xanadu is the Original Hypertext Project which was started by Ted Nelson.