There are a few issues I have with this software. I have had problems with recording my guitar. I don't know if it is the software or the amp but it seems that the recording speeds up and slows down. It makes things difficult when I am trying to right songs. I enjoy Metal/Rock/Hardcore. Witch requires heavy distorted guitar which GarageBand doesn't exactly supply. It is more fun to record yourself playing than using software anyway. Another issue I have with it is the fact that the strings take a long time before they start playing. I have tried to make "Epic" sounding songs that require instant play from the strings and it just doesn't happen. There are ways around this but they are time consuming. One of the major problems is if you have "Too many instrument tracks". You will be trying to play a project through and it will stop in the middle of it popping up a box that says "Part of the project could not be played".
Overall they have made music making more easy for the consumer with this software. All of my friends that have Macs use GarageBand. It is fun and easy to use.