I hope people will read it correctly, particularly the learning part... Ie. they won't read it: Always to your own code!
There are several cases where one shouldn't re-invent the wheel: the most obvious is lack of time. If my manager asks me to add PDF export to our Java application, and do so while meeting the deadline, obviously I won't download the PDF specification and start coding the implementation: I just will hop to iText library (at best look at some alternatives) and learn how to use it.
While I would love to do the former, probably lot of fun, it isn't realistic, we don't have years ahead of us.
Now, in my free time, I will code my own algorithm of Delaunay triangulation, because it is fun and interesting and I will learn a lot in the process, and I have no deadline and bugs are mundane here.
And as others point out, to re-invent the wheel, you have to have some capacity to do it right, at least if you must use it later... I wonder how many posts on StackOverflow ask: Is my regular expression of e-mail validation right?. Often, it is just No, even ignoring extreme/rare cases.
I remember your post where you state It is my work, I live out of it, I must code it myself and master all I do. It was about sanitizing input, if I recall correctly. I must agree here, and I suppose you did lot of research, looking how others did, what crackers uses to attack, etc.
Now, you are not a fool and use good ready-to-use products, like WMD and such.