Are intentional sins somehow "worse?" There seems to be a sense among many Christians that sins are somehow "less bad" if they were accidental. Leaving aside two salient points, namely:


The entire point of grace is that sins are forgiven. 
That all sins are equal in the sight of a perfect God


the question is then, how do people get to the place where they look to the intentionality of the sin?

Are there denominational confessions that differentiate? Is there a biblical basis for making intentional sin somehow worse?
First, I don't think:


  That all sins are equal in the sight of a perfect God


is a biblical statement:


  Jesus answered him, "You would have no authority over me at all unless it had been given you from above. Therefore he who delivered me over to you has the greater sin." (John 19:11, emphasis mine)


All sin is offensive to our holy God.  I don't think the Bible teaches all sin is equally offensive to God.

To answer your question, this parable seems to indicate that intentionality does matter:


  And that servant who knew his master's will but did not get ready or act according to his will, will receive a severe beating. 48 But the one who did not know, and did what deserved a beating, will receive a light beating. Everyone to whom much was given, of him much will be required, and from him to whom they entrusted much, they will demand the more. (Luke 12:47-49)


So, what are the implications of the believer?  Sin is like an infection, the more you partake of it, the more corruption it works on your soul:


  Do not be deceived: God is not mocked, for whatever one sows, that will he also reap. 8 For the one who sows to his own flesh will from the flesh reap corruption, but the one who sows to the Spirit will from the Spirit reap eternal life. (Gal 6:7-8)


The person who is sinning intentionally is working harder at sowing to the flesh and will therefore reap more corruption.