To my knowledge (someone correct me if i'm wrong) you will loose all your music/videos/podcasts as you caun't sync from your iphone to a new iTunes/Computer that dosn't have the origional content.
Data like contacts and bookmarks can be re-synced from the iPhone as there is an option within iTunes for this.
The only time you should be worried about loosing your jailbreak/unlock is if you restore your phone, which wipes all the data off. Connecting to other Macbooks or PCs wont affact your unlock.