[riffraff]

how did you use flashcards? I.e. did you use some "refined" form of spaced repetition or just moved a card at the end of the pile?

IMHO the difference in the quality of learning varies greatly across the paper flashcard/supermemo-ish software continuum.

[dpapathanasiou]

I don't remember which set I tried, but their characters seemed disjointed/random and, worst of all, unrelated to anything I was doing at work.

I just found it better to try to read the reports and memos being passed around at the office, and once I looked up kanji I didn't know, I would tend to remember them, since I'd read them in the context of a sentence.

[wahnfrieden]

You can use flashcards to learn kanji. The problem is trying to learn them without context and by learning their readings rather than by learning the reading via learning vocabulary which use the kanji you want to learn.