Right now I am using Adobe Creative Suite 3 to aid my development, not bothering to update to CS4 due to the fact that while it had a lot of nice features, I didn't think those features were worth the hefty upgrade price. While I can not say whether it is worth upgrading from CS4 to CS5, It seems like it will be well worth the price to move from CS3 to CS5. While I am slowly going to be migrating from Flash to HTML 5, I still think there is enough life in Flash to make one final upgrade. Getting Dreamweaver, Photoshop, Fireworks, and Illustrator also helps but the biggest addition to the package was Flash Builder 4 (formerly Flex Builder) and its integration with Flash CS5.
Adobe, obviously, will not just stand by and let Flash die. The question is what will they do to salvage it? Some suggest turning it into a tool for creating Canvas or SVG code. Others think that new compelling features will be added that the various HTML 5 additions simply can't support. AIR is certainly a factor. While I haven't created any AIR applications yet, that could possibly change. The key question for me, however, is does the added features of a proprietary platform out-weight the open standards enough to warrant its use? HTML 5 is a balancer, but more weight on the Flash side could tip the scale. It seems we are still living in interesting times.