Is it worth it?
By "worth it", I assume you're asking if you'll earn more money than it costs you within a short period of time. To determine that, you have to make some guesses as to what the following values will be when you receive your unit. For the sake of this question, I'll plug in my own estimates for a Jupiter (below):
Knowns
Equipment Cost: ~$7,400 (USD) - after shipping to United States and purchasing a decent power supply
Electricity Cost: $0.128/KWh - based on my actual cost
Power Consumption: 1000 watts (probably going to be lower, but let's just use this)
Hashing rate: 400GH/s
Unknowns
Delivery date: 10/31/2013 - Fingers crossed!
Possible Difficulty: 150 Million - Could be way higher or way lower
USD/BTC: $100 constant - This could vary wildly up or down
Difficulty rate of increase: 50%/month - Hopefully not this high
Now, plugging these values into the btcinvest.net mining calculator, you should break even by the 13th week of ownership. It would no longer be profitable at all after about 40 weeks. Your total profit (after subtracting costs) would be ~$3,670. This equates to a 50% return on investment after 40 weeks.
Of course, 50% increase per month can't be sustained forever. If it ends up being a more reasonable 30% per month, your profits will be closer to 100%.
Also, you may be able to sell the hardware when finished
