You can search for topics or keywords inside your eBook, or out on the Web. Similar to the word look-up feature, this is something that augments the reading experience.
Most of these features are just the tip of the iceberg of what eBooks are capable of. As ReadWriteWeb’s Curt Hopkins opined yesterday, “the e-book format has inherent multimedia possibilities: trailers, background and reference materials, interviews, actors reciting the poems the book contains.”
Those multimedia features probably need to come from publishers, rather than eReader manufacturers.
In the meantime, let us know in the comments what your current favorite eBook features are. Or are you still a paper book hold-out?