Google has updated the Android Market to add support for tablets and smartphones which are restricted to running unoffcial market applications.You can now install Android Market on devices which were previously unsupported and get access to the range of applications which were previously only available on premium Android tablets or phones.
So if you are an owner of an Amazon Kindle Fire, B&N Nook Tablet or own a cheaper tablets from Archos or eLocity.Google Android is meant to be open source. But users being unable to get access to official Google apps restricts cheaper tablet makers of competing against the big players. Now a user can buy any tablet and get the same software experience without having to spend premium prices.
One issue the Android Market will face is when it find an application installed from a non-Market source it will and and fail updating it as it wont have the proper digital signatures. So it is recommended that you remove applications from non-market sources and allow Android Market to get the validated apps on your device.
source - Liliputing