In today's issue of BtoB's E-Mail Marketer Insight, Marilou Barsam, VP-client consulting services for TechTarget, answers the question "Do questions make effective subject lines?". Here's (part of) her answer:

Using a question as a subject line can produce strong results if you follow some simple guidelines:

Know your audience.
If you understand what makes recipients tick, what their priorities are and what motivates them, you will strike a chord with them by asking a question that speaks directly to their specific interests.

Be provocative.
Pose a question that demands an answer. Ask about a controversial issue or industry trend - something that they could not help but have an opinion about because it affects them in some way.

Be brief.
Fewer words are easier to read. A quick question will actually stand out more in the list of subject lines that appear in recipients' e-mail boxes. Use strong words that pop off the screen, but stay away from hype.

Read the full article here.