Glad someone likes it. Is there a way I could submit it when it's done?
Do you use SVN to check out the source code? If you're not on the project yet, I can give you SVN commit access, I'll just need to know your sourceforge username.
The largest issue I forsee with the loan shark is it could be by far used as a quick boost to the early game and then easily paid off in the mean time, unless all goes wrong.
In many games loans are often supposed to be a serious drain to make you consider not getting one
... and also to others discussing this.
I find that in most games with loans, they're so prohibitively non-viable that they're more of a trap to ruin players who don't know any better. I wouldn't mind if they're a usable strategy here. Here you'd pay back with 100% interest within one or six months, which is absolutely brutal by real world standards, but it's actually doable if you have experience with the game.
Here's what I'd do. Keep their expectations brutal, so that it's rough on experienced players, but make the penalties not game-ending if you default. Only let you default once, ever, unless you manage to make amends, but the worst than can happen is that some gang members attack one of your safehouses, and regardless of the outcome of that, the loan shark gives up. And make the penalties sliding scale, so that even that is only for really severe defaults, like the six month $10,000 loan.
You can also give a confirmation when they go to take out the loan. Have the loan shark press you on whether you're "absolutely sure" you're good for it, and warns you that the penalties for being unable to repay him could get violently unpleasant. Give the player an opportunity to back out. After all, the loan shark's not trying to get you to fail to repay him. He wants you to repay. If you're not good for it, he'd rather not make the loan. You could also do what Capital Fish mentioned about giving your character a bad feeling about it.
Other alternatives include installments, and renegotiating. He's ultimately in this for the money -- get the money to him late or on a different schedule, and he'll quit trying to send thugs after you. Just don't come to him crying next time you need money, since he's not interested in unreliable clients.