Is it safe now to develop web application with HTML 5 specifications? or should we wait longer for final standards?
I want to start developing a new project. I want it to be up to date in every aspects. should I wait more for html 5 or I can start programming based on it?
It depends on your audience. If they have the latest browsers then you can start using parts of HTML 5. If you don't have a good understanding of your user base then you might want to use web analytics to understand the capabilities of their browsers. Developers tend to have newer browsers but corporations or schools may not. You should also do some research on HTML 5 and understand if you can get up to speed with it quickly if deployment time is a concern.
It all depends on your audience.
If most of your audience is going to be fairly hip web developers that know to use a decent browser, you are probably going to be fine using HTML5.
However, if your audience is any government institution (school, etc), business place, etc, you might not want to use it yet. My school currently runs on Internet Explorer 6/7, and one of my teacher constantly complains about that "Your browser is not supported" message at the top of Youtube. These people probably don't have any control over the browser they use, and might be a bit behind due to the IT guys.
Find your audience, and use what you are comfortable using with them.
It depends what you which features you want to implement. HTML 5 is a very broad standard covering video, dynamic bitmaps, geolocation, more semantic tags etc.
No browser has implemented all HTML5 features, all have implemented some
This will tell you most of what you need to know about and which browsers support it.
Which part were you particularly interested in? Many people want to use canvas which is the dynamic graphics tag (simulates svg in an element). Canvas works on all major browsers except IE, though support for canvas is predicted in IE9
Use progressive enhancement. A lot of the HTML5 features (application cache, the custom form fields, the extra semantic tags) will do no harm in unsupported browsers (though you might need the HTML5 shiv from Remy Sharp), but give a bonus to users and spiders who can use them. Other features (video tag, database storage, web workers, geolocation) can use workarounds for compatibility with older browsers - the Modernizer library linked by Mark Pilgrim makes this very easy. If your app is usese Geodata, for example, you could use the browser-based geolocation where available and fallback to something IP-based.