Coming from webOS, I never had flash until the Touchpad. Then I got used to it. However, on a phone, I'm not used to it. I'm running the Mango Dev release, so I'm not sure if this was available on NoDo, but this solves the main thing I needed flash for: logging into my bank.
They use a flash based authentication for the "full" browser experience. With webOS, it didn't have the option to tell the site that you wanted mobile experience, in an easy way. With IE9 on Mango, I set it as "mobile" mode and authenticate at the bank. Then I set it as "desktop" mode and refresh the page. Bam, authenticated on the full version of the bank display. Nice little hack to get around not having flash.
That said, I wish we had it. When evaluating Android and WP7, Flash, Audible, and slightly better Voice features were where Windows Phone lacked. UI and basic usability was where Android lacked, so here I am.
For those posted above about "full" desktop experience on Mango, I've also saw issues. There is a company website that my wife uses in her business. It will not let her login, due to not handling cookie setting or redirection properly (I've not looked deeply at the issue.) With the ability to do packet sniffing through USB network connection, I might do this and submit a bug report. They do have a mobile site, and again the mobile setting allows her to get in with that. Although it is more of a hack that shouldn't be required if IE9 was more standards compliant. Whatever this web site does, it works on mobile Safari, Android and webOS phones, but oddly also fails on the Touchpad browser.