I have recently finished a light summer cardigan in a simple lacy stitch - I haven't written about it before because I wasn't sure if it was going to work out, but I'm pleased with the result. So fortunately, I don't have to disown it as a failed experiment , and I am wearing it a lot.
The pattern is distantly based on Blithe by Marie Wallin, that appeared in Rowan magazine 47. But that is designed for an Aran weight yarn (Rowan Summer Tweed) and I have used a DK yarn, and I have used a much simpler stitch pattern, and I wanted to make it longer and not so loose around the waist. So not very similar at all.
Sewing with this yarn was clearly not going to be possible. The advice that I have read for this situation is to use a yarn of similar weight and composition, but I think that in general I would rather use a sewing thread - easier to find a good colour match, and likely to be cheaper too. In this case, the yarn was constructed with an even thread of similar thickness to sewing thread wrapped around a much more irregular ply, so I unspun (?) it to extract lengths of that thread and used that for sewing up. That has the advantage of being an exact colour match, obviously.
A couple of things I would change if I were knitting it again. The sleeves are rather loose, which I think is due to the derivation from Blithe, judging by the Blithe projects posted on Ravelry. On the other hand, that means that I can easily wear the cardigan over a top with sleeves, which is useful now that the weather is turning chillier. The other thing is that the stitch patttern is not symmetric, and so the fabric is not quite square (though that wasn't evident from my test swatch). But I am putting up with that, and hoping that no-one else notices.