How long is too long?

A 20 character domain name?

[zulufox]

I have the perfect keyword phrase (it is THE exact keyword) domain avaliable for my site. The reason it is avaliable is that it is 20 characters long!

#*$!#*$!xxxxxxxxxxxxxx.com

There are 3 words in the domain, but one of them is very long (11 characters).

Is this too long?

[tedster]

Too long for what? that's the important question.
Too long for type-in traffic? sure.
Too long to spell on the phone? probably unless very common words are involved.
Too long for offline branding? depends on the exact phrase.
Too long for links? not hardly.
Too long for resale? Oh yeah!

I think with questions like this it's always "courses for horses" rather than absolute answers. You've got to have your business plan and goals firmly in mind, and that makes a lot of decisions for you. Since you say it's the "perfect" phrase for you - maybe it is.