What are typical legal pitfalls for seed-stage startups?

As a corporate and IP attorney I've worked with a lot of tech startups, and right off the top of my head I can name at least 2 mistakes these companies make time and time again.
First, the founders fail to document the deal they have among themselves, and neglect the basic business paperwork like LLC operating agreements, or shareholders agreements. These are the documents that control how the company will operate, who is responsible for what, and most importantly who owns how much of the company. If there's a falling out among the founders (and sometimes among the first employees as well) but no one bothered to write anything down, the resulting business divorce will be extremely messy. Rule # 1 is document the deal you have with your business partners.
Second, tech startups often fail to adequately protect their technology. This means not only the appropriate IP registrations (patents, copyrights, etc.). It also means protecting the company's trade secrets and other proprietary information through documents like employment agreements, invention assignments and nondisclosure agreements. You would be amazed at the competitive advantages that are lost because a company is not sufficiently protective of its proprietary technology. Rule #2 is protect your assets.
I'm sure there are other pitfalls. Those are the 2 that immediately come to mind.