I might be an outlier, but I don't like slugs in URLs. They make URLs unnecessarily long, often forcing people to use URL shorteners -- completely defeating the purpose. They get awkward when the author changes the title. Other commenters mentioned some tricks to get around this issue, but all involve redirects. Cools URLs shouldn't change in the first place. They don't copy cleanly if you use nonalphanumeric charact…
I haven't noticed this ever being an issue.
At least in Firefox, non-ASCII characters will show as-is in the URL bar, but in the copied URL they will be properly encoded.