Do you send your employees to out-of-house training seminars? Do you think it’s worth the cost?

Two schools of thought - removing the employee from the office to focus on the training is positive; or bring the trainer to your office, which will provide benefits to multiple employees. I advocate the latter approach, but understand the merits of the former.

A very broad question, it depends on the employee, training and company culture.

Sometimes its the only way to train (after you take away their cell phone)...

Philosoohically, the cost of ignorance far exceeds the cost of training:)
If your culture is one of seeking improvement, increasing high performance, you'll probably find training makes sure your employees grow within their roles. But attendance alone does not mean anything. Help your staff plan training that makes sense to both your goals and their aspirations

It depends on the type of training, your employees and also the size of your company. There are now a lot of free seminars offered, especially in the HR and Accounting fields, so the "only" cost to you would be the time spent and maybe mileage. Oftentimes, there are free webinars available as well. Training is required for some employees/professional fields. More important than deciding In-house or outside training would be figuring out if a certain seminar/program actually has value to your employee and the company as a whole.