We need attachments so we can have our layout files hosted locally.

I haven't heard any complaints since I started using Imageshack (for that matter, HP's layout didn't lag for me either), but uploading the pictures to it takes forever, and your stylesheets have to be inline, which means:
1) No dynamic CSS by PHP scripts.
2) Edits don't affect old posts (except for people who use auto-update).
[) Every post contains a copy, which increases the page size.
4) You have to go through and remove all the line breaks and paste this big WALL OF TEXT in your header which is a pain.
Originally posted by Tarale
You can probably get pretty creative. I don't think I've ever had any problems with my layouts breaking the pages, and I tend not to hold back with my code. At all.
It's just important to test thoroughly in various browsers first. 
The biggest problem I've had reported to me were some font size weirdness issues in a particular build of Internet Explorer, but I didn't break the actual page or anything, just had some small text.
I've found there are basically three rules to layout coding:
1) Using position: relative to move more than a very small distance = your element will appear in a random place on the page.
2) It won't work in IE. If you're lucky, it won't be a big problem, but there'll be some stupid glitch.
[) What you see in your local test file may not always match the board. I had to add a border to the top of my post box, below the title bar, or else there'd be a big gap there.

(I'm not counting "use common sense" and "code properly so it doesn't break other things" because those don't just apply to layouts, and "you can't use Javascript" falls under common sense.

)
Other than that, you can basically do whatever you could in an HTML page if you know how to pull it off.
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