The Good: Rosetta Stone is a very user-friendly, low-stress program that will teach you a lot of Arabic vocabularly over time. The format is very simple (a good and bad point)- You get four pictures on the screen and either a written or spoken phrase beneath. Match the phrase to the picture and you're on the way. Very good for association and vocabularly drilling, and pretty easy to use, so you can play with it throughout the day without having to devote a lot of time to "studying." Also, you would be surprised at how creative they can get with the "match the picture" format; all kinds of situations you wouldn't think possible.
The Bad: First, the price. This would be a great $70 program, but the $170 tag is really pushing the envelope. Also, although this program is sold everywhere, the company seems to be pretty rigid on the price- always advertised as $195 but offered for some type of discount at $170. On the other hand, there are a lot of lessons in the program and they go pretty far into the language, so unless you are sure you are going to stick with it, this is a big investment to make and then give up after a few weeks.
Next, this program cannot stand alone, especially in Arabic. For one thing, it does not teach Arabic script, you need that before you start (see Awde's book on the Arabic Alphabet as the best choice for that). Second, it does not teach grammar, just word association, and you should be aware that Rosetta Stone uses the exact same lessons for every language, they are not tailored to the pecularities of Arabic. You absolutely need an Arabic textbook to accompany this, or by lesson 4 you will be lost (Smart's Teach Yourself Arabic is the simplest and cheapest). Last, the voices used (unless they've changed them recently) are very strange. Some of the other languages are good, but the Arabic speakers sound like greeters at Disney World. If you've been to the Middle East, you will recognize how silly they sound.
Bottom Line - if the price doesn't bother you and you use it to supplement existing Arabic study, this is a great program for drilling and vocabulary building.