What are the advantages of flash, to say HTML5 or any other similar platform. If I was a developer making an internet application what are the advantages/disadvantages of flash?
The only advantage of Flash is that it is here today. Web developers can and do use it today. Flash is used in video, banner crap and also for site navigation. If you do a search for web templates, you'll find a lot of pre-coded templates available for sale at reasonable prices. You'll also find the vast majority are Flash sites. So an advantage is the availability of pre-coded templates - most containing Flash elements.
HTML5 is not ready today for web developers. It's a scripting code developed by Apple and Google. You see HTML5 on YouTube (owned by Google) and some selected sites that are also owned or controlled by Apple or Google. There are no HTML5 editors available today for the general web developing market.
HTML5 is tomorrow's web technology, but tomorrow is supposed to be around 2012 before general release. When an editor becomes available, it should have pretty good adoption rates. But currently, there are to many exceptions in the code to make editors possible. I'm sure it will all be worked out, but today is not that day.
You can use simple HTML, CSS and Java-script to accomplish a lot. You'd have websites that were devoid of the "pazzaz" to which we've become accustomed. The content would be the same and there would be much less "intrusion". This would be welcomed. But advertisers are sneaks little bastards and I'm sure they will give you pop-ups in HTML5 also.
I just re-did a website to accomodate Lord Jobs vision of no-Flash. The new site doesn't have quite the dynamic look that the Flash site had (no banner ads on the old site, in fact, no ads at all). But I must say the new site loads in a quarter of the time and is completely viewable on the iPhone (before I had to use a re-direct to an iPhone compatible site). I don't really care that much about catering to the iPhone, but eliminating the Flash elements makes the page load so much faster, I think this is a huge benefit.
I'm still wishing that Flash would be supported i the iPad (which it never will). The web will be slightly duller without Flash, but will be a lot nicer. Of course HTML5 may very well offer the benefits of Flash without the overhead security problems. It's still a couple of years before we'll really know.