For casual drawing on an iPad, Penultimate ($1, direct) is second to none. It's fast, friendly, flexible, and a bargain. If you've ever doodled in a notebook, using the app should be second nature. When it comes time to share, you can e-mail a sketch or an entire notebook without leaving the app, or pipe your pad through a projector for group collaboration. While the app's touch-based sophistication will no doubt impress consumers, but when paired with a touch stylus like the Kensington Virtuoso ($24.99), Penultimate can scale to the professional demands of engineers, architects, and industrial designers.
Broad Strokes
Penultimate's interface looks familiar, though if there's any uncertainty, an interactive walkthrough takes just a couple of minutes to complete. You'll write in a virtual notebook, filled with blank, grid, or lined pages. The tools, a pen—fine, medium, or broad tipped, in six shades—and eraser follow your finger across the page. New pages appear when you flip forward by touching the top corner of a page. This feature showcases the app's speed: I found flipping between pages nearly as smooth as thumbing the pages of a physical book.

Also worth mention are two controls through which you can improve usage. From the settings gear you can move the toolbar—buttons for clearing a page, writing, and erasing—from the bottom of a page to the top. There's also a clever feature called Wrist Protection, which, if turned on, automatically disregards stray marks from a resting wrist. Sometimes, especially when doodling, Wrist Protection can be overly protective, ignoring quick swipes, but when it comes to writing, it's a must.

Finger Painting
I created several projects, what Penultimate visualizes as and terms them as "Notebooks." Accessing different notebooks is as easy as returning to "My Notebooks" and swiping through the covers. Inside a notebook, I could create as many pages as I wished. One notebook, for work, had 22 pages; another, for friends, had 5. Unlike a notebook that comes in one style—blank, lined, or grid—with Penultimate you can alternate between the three: I took some meeting notes on a lined page, switched to grid for a product sketch, and brainstormed on blank.
Also adaptive is the stylus: Clicking the pen button, I alternated between the three tips and six shades. Certainly, I wish there was more: More styluses and color controls would render Penultimate a more capable artistic companion, akin to SketchPad HD ($.99) or Adobe Ideas (Free). At first I made plenty of mistakes, and my tendency was to use the eraser; however, I soon realized that the "Undo" button inflicted considerably less collateral damage on my sketches.
I'm certainly not an artist, and the only thing worse than my doodling is my penmanship. That said, I found the iPad display didn't make my handwriting any worse (if that were possible). Writing with an index finger proved remarkably similar to—and equally atrocious as—using a pen. Penultimate is fine for quick notes, but I wouldn't recommend it for heavy writing. Without Optical Character Recognition (OCR), Penultimate is a less apt note taker than an app like Underscore Notify ($1.99).
I also wish the app supported multiple points of input. I understand that one doesn't, after a certain age, use more than one pen simultaneously. However, a setting to activate Multi-touch sensitivity—akin to Wrist Protection—could enable users to create richer canvases.