I attended Structure 08 last year. Structure 09 has been announced for June 25th (San Francisco). Based on my experiences of attending last year’s conference, I do recommend that those involved in “cloud computing” (including general SaaS operations) attend at least once. It’s good to hear varying points of view, learn about what’s new, hear some arguments, Q&A, and validate (or unvalidate) what you’re currently thinking.
There are some big people/companies on the keynote list, including Amazon, HP, Yahoo, Savvis, Ebay, Facebook, Level3, and LinkedIn. It’s worth it just to hear what they have to say.