Flash is fine... but just like with any other technology, there is a quite large group of people who don't know how to properly use it and they end up creating a ton of poor quality content. The technology itself is Ok, but the way many people use it is far from ideal... As others have pointed out, there are ways to block it if you really want to...
Most people dislike Flash just because Jobs had a problem with it ( business you know... everyone is protecting his own stuff ) and said that it's "Evil". There are definitely really, really, really badly written Flash application out there too, but the same can be said by all the other technologies as well... Adobe sucks at PR and they were never really capable of cleaning Flash's name as a technology. Many people "hate it", but almost none can really explain why ( nor do they understand )... if something crashes, is slow, eats up battery, etc. it's easier to just point fingers at the thing you see many others pointing their finger at than actually sitting down and try to understand what happened. 🙂
Flash is Ok, but it is far from perfect and there are definitely many crappy applications written by complete beginners out in the wild... just that things aren't as "horrific" as some try to make them seem. Many companies / banks / institutions / etc. use Flash based applications on a daily basis... if Flash was really that evil, it would have died out ages ago 😉