^Well, from what everyone is saying, you all make it sound like Indonesian is really really easy. I'm an Indonesian person who did Indonesian SL, and here's my take on guys / girls learning Indo. My theory is YES, that most people improve a lot at a short time, even if they don't put a whole lot of work. But getting fluency at Indonesian is bloody hard, akin to an Indonesian person learning English for the first time.
It's not hard to improve, that much is true. But trust me, when you don't continue to speak, write, or read Indonesian constantly, there is no way that you can just 'piece it together' or 'cruise Indonesian'. It's definitely not a joke, and being fluent at Indonesian is quite hard.
If you've ever gone to Indonesia (well, probably Bali for most of you), try talking to a native fully in Indonesian for a few minutes. It can be quite hard to talk to the person, and also listening to the person. It's because you're not used to it. Try listening to Indonesian news on SBS. I can tell you there's a 99% chance that someone who's not fluent in Indonesian will not understand the whole meaning of news that has been said, because they speak real fast. As for reading and writing, it's definitely easy to write simple essays, but when it comes to reading news (such as Kompas), the same thing happens: you might understand some of the information, but the rest is hard to understand.
EDIT: Need to address OP's question number 2.
Well, the only practical utility of Indonesian is if you want to work in something that requires Indonesian (Indo teacher, translator), you want to have a holiday in Indonesia (STOP ONLY GOING TO BALI / JAKARTA PEOPLE! GO TO OTHER PLACES IN INDONESIA), or if you want to actually live there.
Oh btw, if you're planning on learning Indonesian, I'm going to point out the fact that when you hear other Indonesians speak with each other, you're still not going to understand everything even if you're fluent. That's because
A. They're using colloquial words. Most common example is substituting 'tidak' with 'nggak'. A less common example (that I use, sometimes), is substituting 'tidak' with 'emoh'. All of them mean no, but just in different words.
B. They're mixing their dialects with proper Indonesian. There's lots of dialects in Indonesian, and they all have different words. For example, I can't understand / speak Balinese dialect, since I'm from Central Java. But I can speak Javanese, and I use a mix of Javanese and Indonesian plus colloquial words when talking to other Indonesian people.
Trust me, there is no way that an Indonesian person will ONLY use proper Indo when speaking. The only time they'll do it is when it's a formal ocassion (like job interview), or talking to someone who's not fluent at Indo.
And sadly, I don't think that there's an awesome cultural phenomenon that increases appreciation of Indonesian language, unless you like playing gamelan, making batik, playing / making wayang etc. It's unlike say, Japanese. I mean, if I could be fluent at Jap, I can watch anime and read manga without subs. AND THAT IS COOL.
SOZ, BIG RANT. But it's about Indo...