Even though I have been slowly weaning myself off of the newer Sony cameras, I still have some Sony devices that need memory pro duo cards. There are some advantages and a few disadvantages, namely the cost and availability. Sony's memory format averages 30 to 100 percent higher prices for the same capacity of SDHC cards. While that sucks, if you have a Sony Camera or a PSP there's not much you can do about it.
To that point, both the new Sony Cybershot DSCT300 Digital Camera and upcoming PSP God of War Entertainment Pack will benefit from any of these memory cards. Both of those devices, along with most Sony devices for that matter are only comaptible with the memory duo platform.
But like I said, if you need one of these cards, there are some advantages especially if you get a Mark II card. Namely, the performance speed of the mark II format is about 50% higher than the fastest available SDHC card at the moment. The rating is for 36 MB/s and what I've seen through some basic tests seems to indicate real performance close to this. In fact, the solid performance has to be the biggest pro for these cards. So while it sucks to have little choice, when you factor in the premium performance it's easier to swallow.
The 2 and 4 GB cards are a better value than larger capacity ones right now. Sometimes you want the largest card you can get, but till the 8 and 16 GB cards come down I see no reason to buy them. Not to mention, this isn't for my primary camera but for an older one that I use as a backup.
Make sure your device is compatible with the card. Some older electronics aren't compatible with larger capacities, although in general Sony has been better with making these guys backward compatible than others.
It's always a good idea to have several extra cards on hand just in case. This 4 GB card is a nice performer. If you have a high capacity camera (10 Megapixels or more) and are storing videos or RAW images, the extra cash for the 8GB card may be worth it if the price is right. Or you may want to step up to the larger 16 GB size that is now available. But if you wait a little longer you can save yourself some cash. I have to take off at least 1 star for value, but in terms of performance I couldn't be happier.