Did you check with your local software association? Sometimes they'll have good deals because they've partnered with a carrier who understands our biz. (We've got links to dozens of associations on our Industry Groups page.)

Also: I know nothing about these guys, but they came up in a search: http://www.techinsurance.com/ and http://www.insurenewmedia.com/ -- both claim to specialize in E&O/liability for tech companies.

(Of course, the fact that they came up in my search could simply mean they've got good webmasters -- but it might be worth getting free quotes.)

Good lead, Tony -- thanks. Unfortunately, they don't write policies for the US. With a little research, I found that a number of US companies offer "cyber liability" and "social media" insurance -- googling should turn up providers. The two I mentioned in my earlier post claim to specialize in IT companies -- but again, I am not endorsing them.