In my previous post, I mentioned that the Modbook can be a bit of a gas guzzler, even while in sleep mode. There have been posts on the ModbookArt Forums about varying experiences regarding this subject. It all really boils down to usage. Some have gotten really good mileage using their Modbooks in a variety of situations including general use.
However, it seems apparent to me (although not unexpected) that running apps like Photoshop will drain the juice out of that Macbook battery faster than usual. For instance, starting at a 100 percent charge I sketched with Photoshop along with Adobe Bridge for 40 minutes and the charge went down to 73 percent. (I've done this several times and the average is about 20-30 percent battery consumption per 30-45 minutes of use)
For one full hour the battery went down to 58%. This averages to about 2 hours of sketch time per charge. Once that fan starts to spin, expect your battery life to go south.
Now 2 hours isn't bad. However like I said previously. Plan on an extra battery if you plan to be away from home base for a while. Most coffee houses (like Starbucks) and restaurants don't mind you plugging in as well. Just plan on ordering some Java to avoid a dirty look.