That's not the only "speed" increase either: the new cards are 802.11n compatible, meaning that if you have a "Wireless-N" Wi-Fi network, it will transfer your pictures very quickly. Previous cards only worked on "G" speeds, which made the transfers seem very slow. Videos can now also be wirelessly transferred as well, removing another previous limitation.
It still boggles my mind that they can fit 8GB into something so small, but since it also has RAW image support in the Pro X2, the more space the better. A new "Endless Memory Mode" will automatically remove pictures and videos after you have uploaded them to ensure that you don't run out of space on the card. You can control whether or not to use this feature at all, and if you do enable it, the companion "Eye-Fi Helper" application lets you set how much space to set aside. For example, if you say "Keep 4GB open" but then take 6GB worth of pictures, it will upload all 6GB and then remove the oldest 2GB worth of pictures from your card. If you are like my mother and keep every picture you've ever taken on the camera, you can set it for a lower amount. If you are like me and want the pictures off the card once you know they are safely uploaded, you can set it for a higher amount.
Geotagging via Skyhook is included with the "Explore X2" and "Pro X2" cards (see a chart of differences between the different "X2" models here). The Explore and Pro cards also come with one year of "Hotspot Access" available at "tens of thousands of locations, including Starbucks, Barnes & Nobles, restaurants, major hotels, airports, and more." The cards will upload from any open network. Note that you have to configure the card to access hotspot and "open" networks, and it will not work with open networks which require some sort of login.
About the only blemish in the entire Eye-Fi experience for me is the "Eye-Fi Center" software. As far as I can tell this is some sort of GUI "shell" which wraps around a web service. (Update: it's an Adobe Air app.) It's fairly craptastic. The UI seems unpolished, although very colorful, and it's more difficult to find some settings than it needs to be. That is a minor complaint, however, compared to the all-too-frequent problem of telling me that I need to insert a card which is already inserted and which has been inserted for some time now and which the "Eye-Fi Center" software has been accessing up until the point when it decides, for no particular reason, that it is no longer inserted. Most of the time the problem is solved either by relaunching the software or by ejecting and re-mounting the card in its USB reader. In the grand scheme of life it is a minor issue, but it happens far too often.
One final feature note: the Pro X2 also supports "Ad Hoc," meaning that if you are out somewhere without a real Wi-Fi network but only your laptop, you can create an Ad Hoc Wi-Fi network on your laptop and have the pictures upload to your laptop without a router.
As someone who was very disappointed with the first generation of Eye-Fi cards, I am hopeful that the second generation "X2" cards will finally live up to all the promise. The ideas were always solid, but now the technology has finally caught up. Obviously I've only had the card for a few hours, but I look forward to putting it through the paces. At $150 there is no doubt that you are paying a hefty premium for the card, but the feature set makes it worth it to me, if for no other reason than this one: With an automatic upload to Flickr and my hard drive, every picture I take is automatically backed up off-site as soon as I get back to my computer.
Note: This review is based on a unit I pre-ordered a few weeks ago, and paid for myself (my birthday is coming up), not a review unit. If you look at Amazon's web page for the Pro X2, it says that it won't ship until April 6th. This is Amazon's way of saying that it is backordered (a word that Amazon does not seem to like), which you can confirm at Eye-Fi's webpage. Pre-orders began shipping last week.