How do I hate Flash? Let me count the ways!
1) It leaks memory. All the time. Memory I can't get back without restarting my browser
2) It's designed for content creator dickheads only. When those delightful animated/video/audio adverts start up, where is the stop button? Where is the mute button? Where is the dont fucking auto play these shite adverts button.
3) It crashes. Lots.
4) It's super slow, and succeeds in making browsing the web super slow. Every page with one of these shite flash widgets on (think BBC news, 2-3 audio clips embedded in each page) makes the page visibly slower to load, as the browser does arcane jiggerypokery to try to load this bug ridden piece of shit in a safe enough manner to allow me to hear the dark lord Mandelson speak for 1 minute.
5) It's poorly written code (see 1,3,4) that is installed across almost every PC machine in existence. This makes it a large attack vector, just like Acrobat Reader (Adobe secretly owned by RBN?)
I could go on, but I won't.