Jo's very anti-opensub.
The Negatives:
It's a long haul, 99 times out of 100 resulting in a no. The kicker is the 3 month exclusive, meaning you can't send it to anyone else while it's sat forgotten on someone's hard drive. Not many agents require this any longer. Angry Robot didn't in their last open, that I recall.
It's a lot of faff.
You won't have an agent to navigate through a contract if they offer.
You won't get personalised feedback.
Checking on your subs progress becomes an obsession.
You plan world domination even though you KNOW the chances are slim.
You'll probably end up with a boiler plate contract.
You'll have to pay SOMEONE to look over that contract.
We haven't even got to the issues of marketing that book 'alone' yet...
The Positives:
It takes a certain commitment to believe in your work enough to send it in.
DAW is a big name - its published some great stuff (Check out Mike Brooks' space western Kieko series, starting with Dark Run, anything by Kate Elliott if you want examples)
You won't have an agent taking 20% of your advance. (US counts as foreign soil, folks)
A 'yes'
can help in finding an agent.
You dodge a gate or two going direct to the publisher.
As you can see, the negatives far out way the positives. Agents make things so much easier-
but not necessarily faster. 
