Active Networking adds programmability to the elements of the network, most aggressively by using programmable packets, or capsules. ANTS [22, 21] and PLANet [10, 8] are the most mature examples of capsule-based systems, both having been publicly available for several years. This paper presents our experience with these systems and the lessons they hold for the future of capsule-based Active Networking. The paper focuses on four key issues: flexibility, performance, security, and usability. We consider how ANTS and PLANet address these issues, noting that despite substantial surface differences, both systems identify similar key problems and use closely related solutions. Based on our experience with these systems we conclude that capsule-based systems can achieve useful levels of flexibility, performance, and usability. Many aspects of security can also be adequately addressed, but some important problems related to denial of service remain as open problems.