I've been in dual system mode for 3 years now with a 27" iMac plus a 13" Aluminum MacBook. If you can truly separate everything you do between the machines, that's great. But I personally haven't found that possible or even desirable. I use the iMac when I can, desktop ergonomics are superior to a notebook computer. I use Chronosync to synchronize folders between the systems -- I organize via project and projects that I perform away from home are the ones that I synchronize.
There is great appeal to just having a single system, because you have everything at your fingertips without worrying about syncing. To get best use of your existing MacBook Pro,
- You must set up to back up your system on a regular basis. With a MacBookPro the easiest way is to get a TimeCapsule, although it's better to also have separate cloned backups that you can save "offsite" in case of theft of your computer and TimeCapsule or total loss in fire.
- Make a "docking station" so you get the ergonomics of a desktop computer when you are at home. If you have the cash, get the 27" Thunderbolt display, wireless keyboard and mouse. Having that big display is very useful for showing multiple apps at once.
- Max out the RAM and hard drive in the MBP. You can, indeed, do everything on it, just not as fast as a top end iMac. Mine has Xcode, Java, and Qt development software, and all the apps I own for video production, image processing, graphics and documentation. Frankly everything that's on my iMac except for some infrequently used Virtual Machine images and archival (completed) projects.