How often I Can Update my Application on App Store?

Highly unlikely.

Apple's review time for a completely acceptable app update varies from less than 2 days to over 2 weeks, and a developer has no control over that length of time. That will limit the rate of updating any app to Apple's pace. Trying to update more often than this will put your update back at the end of the queue and slow down your approvals, and thus App store releases even more.

Somewhere, maybe a developer's talk, they may have recommended non-critical (for bugs) updates no more often than once per month.

For more frequent updates of content, see Apple's WWDC 2010 video on data driven app design, and consider having the app update certain content from your web site.

No you cannot change it every 2-3 days, because there can be only one version in review of a given application. If a binary is submitted for review and you upload a new version, the old binary is thrown away and the review process starts over with the new version.

So you loose your position in the review queue each time you submit a new binary while the old one is already submitted but not accepted yet.

Not really.

It usually takes Apple 7 days to review an app and if you upload a new update before the old one has been reviewed you go to the back of the queue. If you need to update your app more frequently than every ~7 days you should look into setting up a web-based update mechanism. Obviously, you won't be able to update any code this way, but you can update content as much as you like.