If you believe the rumor mill, we are likely to see new MacBook Pros from Apple on any given Tuesday. Those machines will likely come in the same 15-inch and 17-inch size delineations as the current models. If you look at the pictures (below - from Engadget), you'll notice that there isn't much in the way of footprint size difference between the MacBook Air and the 15-inch MacBook Pros.
While differences in thinness (half inch) and weight (two pounds) are obviously big concerns for the mobile road warrior, most professionals would rather have the larger (15.4 vs. 13.3 inch) screen, the faster processor, more expandability and more storage space.
The new MacBook Pros are likely to get the new, flatter keyboard style and larger multi-touch trackpad that the MacBook Air currently has. Additionally, the MacBook Pro should recieve the latest 45nm processors from Intel - which are much better on power usage than the previous 65nm processors (the MacBook Air uses the previous generation 65nm processor in a smaller package as well).
If Apple adds built-in 3G/WiMAX to the Pro package or outfits it with an energy-saving SSD/Hard drive hybrid model, it might be the deal-breaker for a lot of would-be MacBook Air customers. That possibility might be reason at least to wait and see if you are shoppting for a new MacBook Air/Pro. If not this Tuesday, maybe the next. Or the next..or...