Putting special characters in the title should have no adverse effect on the layout or functionality.
Special characters in the post title have been known to cause issues with JavaScript when it is minified, especially in the admin when editing the post itself (ie. issues with metaboxes, media upload, etc.).
The 45-letter word was coined to serve as the longest English word and is the longest word ever to appear in an English language dictionary.
A few things to check for:
The following CSS properties will help you support non-breaking text.
-ms-word-wrap: break-word; word-wrap: break-word;
This post has no title, but it still must link to the single post view somehow.
This is typically done by placing the permalink on the post date.
This post has many tags.