As the internet grows older, it gets more crowded and internet real estate a.k.a. domain names get snapped up left and right. It gets harder and harder to register a short domain name, and even the long ones are taken too!
Oftentimes we are faced with a situation on whether to choose a domain with a dash or without a dash (hyphens).
According to Google engineer Matt Cutts, Google is generally neutral on the dash issue.
Is the domain name too long?
A short domain such as punkrock.com is fine and easy to remember without the hyphen, but gadgetreviewsonline.com is a bit harder to read when it appears on the SERPs.
Will the domain name result in a pun?
Be careful with domain names that have two or more words that are not hyphenated. They may sometimes lead to a very interesting or a damaging pun. ExpertsExchange.com (ExpertSexChange.com) and PenIsland.com (PenisLand.com) are just two examples of how domain names can go wrong without hyphenation.
Will the domain name be easier to remember with or without the dash?
This is much left to your own discretion. Generally, long URLs are easier to read with dashes.