When I am using Ubuntu for commercial reasons, do I have to pay Canonical?

I made application which use Ubuntu, when i shift it, i will install Ubuntu myself and install application myself as one unit, i can have more unit for selling it all depends based on my marketing and budget.

In that case i have to pay to Ubuntu (i was not aware of this before just discovered today and getting confused now)? Does this mean Fedora/Archlinux should be the choice if i do not want to pay such?

Ubuntu policy says:

http://www.ubuntu.com/aboutus/trademarkpolicy

Restricted use that requires a trademark licence Permission from us is necessary to use any of the Trademarks under any circumstances other than those specifically permitted above. These include: Any commercial use. OEM services

http://www.canonical.com/engineering-services/oem-services/oem-services

What will be the price like this service? Or is that not applicable for Ubuntu 11.04?

Follow up:

That was misunderstanding to me, i am actually using Ubuntu as operating system but i fall in to this model, where i just do remix nothing special.

Derived works. The ability to customise Ubuntu to meet your specific needs is one of the great strengths of free software in general, and Ubuntu in particular. While we encourage customisation and derivation of Ubuntu, we must balance that freedom with the integrity of the Trademarks and the quality which they represent. To help reach that balance, we have established the following guidelines and definitions. We recognise and encourage the concept of a “remix.” Remixes are derived versions of Ubuntu, and it is intended that any software and hardware certifications will apply to a Remix. Therefore the changes from the official Ubuntu product must be minimal to be permitted to use the Trademarks. These changes can include configuration changes through the existing Ubuntu configuration management tools, changes to artwork and graphical themes and some variance in package selection. In general, a Remix can have applications from the Ubuntu archives added, or default applications removed, but removing or changing any infrastructure components (e.g., shared libraries or desktop components) will result in changes too large for the resulting product to be called by a Trademark. Note that if the nature of the product's divergence from Ubuntu changes, the Remix naming and Trademark use may no longer apply.

The trademark policy only applies if you wanted to the use the word "Ubuntu" in the name of your product - say you called your service "Ubuntu widgets".

However if you have your own name then you don't need to pay any money to Canonical (the holder of the Ubuntu trademark). You can use as much of the Ubuntu software and platform as you want without paying a penny, though you can pay for support.

Its Linux, read the GPL and stick with what it allows you to do and you should be fine. A more simplified take is this don't sell someone elses hard work as your own, GPL protects authored code abuse but doesn't restrict you from doing what you like so long as you contribute and give proper credit. That is essentially the whole idea behind open source. Trademarks usually protect naming conventions or logos as long as you don't use them or use your own you should be fine.