Certainly a good read- <p>While I tend to be a bit of a details oriented person when it comes to UI, the most important aspect is reducing friction to the user.<p>If a user has to go to your website, download a plugin, wait for it to install, restart their browser, and then go back, you're going to lose them.
This is the same problem when it comes to downloading an application. You want to make it as easy as possible to get things going, as quickly as possible.<p>Ajax gives users this- Flash is useful, and with Flex may gain inrodes into whole-application development, but It's still hairy- While flash is installed in a huge portion of desktops, most of them have old versions..<p>Using it also ties you to technology owned by a company other than you. This is a key point- Look what Adobe has done with Acrobat- It's a great format, but for YEAR it got slower with each revision..
If this happens with Flash, there's nothing you can do about it. It's a closed standard, and you don't own it.<p>At least with browsers, users have a choice of implementation..<p>Adding Flash adds a layer of abstration- Each time you do that, you lose a bit of control.<p>I'd rather use a Ajax toolkit like GWT- Even if Google screws up, it's OSS, and I can fork from the version that worked well for me.