Greg Warren and Carlos Lopes have over 10 years of experience with XP practices. Some of the key lessons they've learned include estimating at a high level instead of precise story sizes, using judgment over rigid processes, focusing on being agile instead of just doing agile practices, dropping practices that don't provide value, accounting for real project factors like scope changes when measuring velocity, involving QA early, thinking long-term, avoiding false panic, and being willing to answer questions.