comScore's press release...

Mobile Broadband PC Data Card Subscriber Growth Decelerates in Q4 2008 as Consumers Pull Back on Discretionary Spending

...reports that after 6 consecutive quarters of double digit growth (between 11% and 28%) starting in Q2 2007, sales of 2G/3G data cards slowed to 5% in Q4 2008.

As their report summary notes:

...deceleration in subscriber growth during Q4 2008 coinciding with the economic downturn, an indication that mobile broadband service may still be seen by many as a luxury rather than a necessity

There's nothing wrong with the cards, of course. Even their prices are generally reasonable. The problem lies in the recurring cost (high) associated with them and level of service (low data caps). The wireless phone carriers need to rethink the way they market 2G/3G data service for netbooks/notebooks as well as WiFi hotspots or they may find themselves ripe for obsolescence as the world emerges from the current economic downturn.