Rayleigh-Benard convection has been a workhorse system for the precise study of phenomena in pattern formation for over 30 years. In the 1990s experiments became available in which very large aspect ratios could be obtained; ratios of lateral size to height of between 50 and 150 were realized. Further, computer acquisition allowed for the accumulation of thousands of images and their subsequent analysis using sophisticated image processing. From these advances came the extensive investigation of spatio-temporal chaos in large domains. In particular, two problems were of the greatest importance: spiral defect chaos in non-rotating convection and domain chaos in rotating convection and in electro-convection. With an emphasis on experimental results, I will review some aspects of these two spatio-temporally chaotic states and will consider unresolved questions that remain today.