I haven't heard about patent trolls going after ebook publishers, but if you use images in an unauthorized way, that can expose you to lawsuits.
You have probably seen the verbiage: "This is a work of fiction. Names, characters, places and plot are products of the author's imagination. Any resemblance to persons living or dead is coincidental." It's probably good to include language like that.
Acknowledging trademarks is also sensible.
Most of these legal hassles are best covered by contracts. A publisher can require the author to assume responsibility for copyright infringements, but practically speaking, the publisher has the most to lose.
The question needs to be more specific; are you worried about specific content? Can you describe this content? Or are you worried about being harassed by patent trolls?
If for example you published in ebook form some source code from software like MS Office (or something similar) and the software company became aware of it, most certainly you would be sued (but for good reason).