Hey, DocToxyn here, confessed recumbent bike junkie. Congrats on the purchase, once you get used to it you'll never go back (OK some people do, they never give up the 'bent). I think a lot of the advice you've received here so far is probably true, the position of the body and ability to move around the bike is very different than what you're used to on an upright and therefore it may just take some getting used to. Most experienced riders say you need to put several hundred up to 1000 miles under your belt before the muscle groups required for 'bent riding are developed, even I you've ridden an upright for years. You'll get used to the balance issue well before this, but more muscle means more control and you may find it improves slowly over time. So you can see that there is a "learning/development curve" ahead of you (nothing to be intimidated by though).
First tell me what bike you have - short wheel base, long wheel base, compact long wheel base, give me manufacturer and model as well. There are so many different configurations that then determine how stable they may be under hands free control. Once we know this, then we can start talking about bottom bracket to seat height ratio and length of wheel base and other steering and handling-related parameters Having said that, I know some people who can ride without hands on certain models, I can pull it off for a short distance on my RANS Rocket, but most choose not too. The other thing to think about is, what is your need to ride without hands? Is it just to grab some food on long rides, or shed a layer, or are you just trying it since you can do it on your MB? You may find that you don't miss it or need it, just sit back in that comfy seat and watch the world go by.
If you're looking for more answers, advice or information, check out http://www.bentrideronline.com/" page, I post there also. Edit: These guys are having some "server issues" at the moment so the homepage is over a year old and the forum doesn't work. Hopefully they'll correct this soon.