I would say Developers are good testers.  Since developer wants to meet the complex requirements first and then address the simpler ones. In addressing the requirements every developer tests requirement with all possible input set making the code to work.
Till integration every developer code works as expected in the development environment. But in integration, there would be different input set to test the functionality.
So, I like to say if developers spend enough time in integration test then tester job would be easy.
I believe integration testing is more important. If there are issues in this environment, then the source should not be moved to testing envi.

After integration testing at least 60 - 65% of the bugs would be reduced.

This is one of the reasons why people moved to Agile methodology in S/w development which forces continuous integration.

Yes, a developer can also become a good tester. I believe its all about attitude of the person. If the person has right attitude of testing the product coupled with qualities like ‘test to break’, ‘strong desire for quality of the product’, ‘attention to detail’, ‘analytical mind’, ‘product and domain knowledge’ he can become a good tester too. Yes, it is absolutely necessary while testing the product he should wear Tester’s hat and vice versa. I know it is difficult but won’t say it is impossible.

Statement is wrongly said....Its a common human phenomena..Whatever work you do, either write code in s/w, cook food or whatever work of your liking, you put your best efforts based on your experience, knowledge and blah blah...and you think this is the best i have done...If somebody says to find flaws in the o/p of your work, you can't.....

Its the other person who can think probably  in a way you haven't thought and may find flaws. The same applies in s/w too....

In developer point of view testing is the process to see software works correctly.
And in tester point of view testing is the process to prove that software does not work correctly. It is not that developers are bad at testing. It is just that they look at things from their perspective & this is what I have seen in my experience. As developer is the person who builds the application. He will look at it only from his perspective. It is the small details he might miss while development. Now it is the duty of tester to have an eye for all the small details and break the application by giving in all types of data and creating all possible scenarios. It is not that who is good, it is just that the end product should be hassle free & that way positions are assigned.....

Dipankar i agree with you because every position has been created for specialised people so a specialised person can justify a particular position. so i would say that developers are good at developing the code but for testing there are people who are expert in testing the coding for which they should only be employed.

The arguements put so far in favour of the topic does not validate the topic.. Instead it only says that "we will see wonders if we put more effort to  testing .. suggesting that the QA guys are not competent in their domain......"

Please come up with more prudent facts and data.. to support your case

The scope of a developer in Testing is to check if his Junits,Nunits have passed and that his code satisfies the Sanity check.

if there occurs any Functional tests which fails, then it surely comes in the universe of the leads and all requirement gathering teams.

I don't know about others.. but yes.. in our team ..it is mandatory for a developer to check that the Unit tests have passed (by Unit we mean code Units checked thru Junits etc).

The functional disparities may be due to insufficient requirements and other facets...

You cannot term the Developer as a "Not good tester" just because you found a bug.

Well, as a developer one is bound to not see beyond the horizon and test his code.. This is just similar to not noticing a ripple in water when you are gazing at the pond for some time...

And btw .. hats off to us.. for providing our tester friends.. to get something to work upon.

If we did all the things... our QA guys would be left doing nothing.. and i do not want that...