I recently started using uMake, an iPad app for freeform 3D sketching. It is an awesome piece of software that has huge potential. I've found it particularly helpful for designing products with organic, complex surfaces. When designing something like a lacrosse helmet, it can be very difficult to accurately translate a perspective sketch to control drawings for engineering hand-off. I strive to make my control drawings as accurate as possible, but there are certain forms that just need to be worked out in 3D in order to fully understand how lanes and shapes transition along curved surfaces. uMake helps get a complex surface concept into rough CAD quickly, bridge the gap between design and engineering.
The app is relatively new, so there are some definite improvements to be made, but they're definitely working hard to make it better. I've already seen a few updates in the 6 months or so that I've been using it. If you're used to working in SolidWorks, you may have a minor panic attack about the lack of control and sketch definition that uMake gives. That being said, this is not a SolidWorks replacement or CAD-for-engineering program. It's more of an underlay generator, for me at least.
I've integrated uMake into my process, and it goes something like this:
1. Create a rough 2D elevation sketch that defines the initial concept
2. Import rough sketch image into uMake and create line work over it.
3. Add 3D line work, using the 2D lines as guides.
4. Tweak the 3D line work to lock-in the form-defining lines.
5. Screen-cap the views that you want to sketch over.
6. Import screen-caps into photoshop to set up sketch template.
7. Create sketch line work over the uMake underlays.
8. Block out the colors, and render away!