When I initially encountered this, I dismissed it as rubbish, but based on a comment by a reader of this blog I've looked into it further and discovered that this may be a case where I jumped to a conclusion too quickly (a not-uncommon occurrence when blogging rapidly).
The category is explained in some detail at Wikipedia:
A type of speculative fiction, paranormal romance focuses on romance and includes elements beyond the range of scientific explanation, blending together themes from the genres of traditional fantasy, science fiction, or horror. Paranormal romance may range from traditional category romances, such as those published by Harlequin Mills & Boon, with a paranormal setting to stories where the main emphasis is on a science fiction or fantasy based plot with a romantic subplot included. Common hallmarks are romantic relationships between humans and vampires, shapeshifters, ghosts, and other entities of a fantastic or otherworldly nature.Romance is not my cup of tea, but since I am a science fiction fan, I need to give this category its due. For a deeper discussion of the genre from the viewpoint of someone in the publishing business, see "What is Paranormal Romance?" (pdf).
Beyond the more prevalent themes involving vampires, shapeshifters, ghosts, or time travel, paranormal romances can also include books featuring characters with psychic abilities, like telekinesis or telepathy.
Paranormal romance has its roots in Gothic fiction.
A few paranormals are set solely in the past and are structured much like any historical romance novel. Others are set in the future, sometimes on different worlds. Still others have a time-travel element with either the hero or the heroine traveling into the past or the future...
Thanks for the heads-up, Kirsten.