I've made plenty of icons and layouts in the past few years. And to be 100% honest, for all that people say to credit icons because that way people can find 'em (myself included), part of the reason you want credit is because you did the work. You took the time to position, resize, crop, color, sharpen, lighten, darken, maybe even screencap, etc. You used your time to make icons for others to use for free, which we all know is a (mostly) thankless task, albeit a fun one, for those of us who choose to do it. The way I see it, the least you can do is say "This person made this, not me!" When I see my icons being used without credit, I feel that it gives the impression that the user made 'em, which is... not true. Also, the key point to me is that it's not hard. >.< I don't mean to be contrary, refuting your arguments that sometimes it's an accident or that life gets in the way, but... I mean, it's also not like the icon maker wants you to write an original haiku about them, they just want you to type their name? XD
With complete journal layouts, I want credit if it is in any way recognizable as my creation. The thing is that coding is an easily mutated beast. I like when people alter what I've made into something that bears no resemblance to the original, because it means they're learning how to code and putting it out there into the interwebs, huzzah! If they're using my layouts direct, or modifying the CSS sheets by using different images/color, it's the same as with the icons. I spent several hours doing this; a credit in a profile is a great way to say thank you for giving us a free, pretty layout! Also, I get more miffed with this than I do with icons, because I spend more time with layouts! It's usually like, 3-36 hours of work, depending on my perfectionist nature. Also, I feel like there's more of my own creativity in them? With an icon, it's mostly just making a photo look great, as complex as this can sometimes be. A layout involves me coming up with an idea, a color scheme, a feeling, and translating that into website form.
A few smaller points on other things that have been discussed already...
Wikicon is a fantastic resource and I love it. It does help us find icons of a PB with ease. It does not help us if we see a face we think is amazing, but we don't know the actor/model/musician's name. The existence of wikicon doesn't make crediting obsolete.
You asked 'when is it stealing?' - it's stealing when the code is exactly the same, to me. The odds of any two people writing the exact same code, in the exact same way are slim to none. I think there's a few other aspects to this debate though. Sometimes you can be inspired by seeing a really great piece of coding, and you take the idea, tweak it, and write new code, 100% yourself, not using anything from the OP. I'm personally fine with this, because let's face it, we all draw inspiration from everything around us, and I'm flattered if someone is inspired by work that I've done. On the other hand... the people who say "I need to know how to make this" - LKJIOJVOAIHWBCAEIUGVBAWUOF - you people ruin the fun for the rest of us. If a layout doesn't have a link to where you can get it, it might be because the person doesn't want you to (duh). I've made layouts for character journals and this journal that I don't want to share with the public just yet. I've made layouts for friends I RP with as presents for being so awesome, and I always let them choose if they want the layout to go up in quibblercons or be 100% theirs. If someone just swipes it, idek, it's so over the top rude, and yes, stealing.
Lastly, erm, not to be rude myself, but... this post sounds a bit like you got burned by someone. All I will say is this: If it was me, I apologize. If it wasn't me, this is the interwebs, and sadly, we gots teh dramaz. I know when I'm in a good mood and I find someone not crediting, sometimes I just don't bother, sometimes I post a nice comment asking them to. If I'm in a bad mood, sometimes it's more terse than I originally intended. I think this is true of lots of peoples, and, it's rarely anything personal. ♥