Even though Apple Mail for iPad can work with Gmail, many Gmail users are bound to find its interface a little too classic and static, especially compared with the Gmail Web interface for iPad. A terrific alternative for Gmail users who want to manage multiple accounts (say, a personal account and a business account) is Ginbox. This simple app handily solves the problem of managing multiple Gmail or Google Apps logins through a single interface, sacrificing none of the straightforward usability that Gmail fans love.
The default calendars in both Android Honeycomb and the iPad's iOS have a certain style to them, but both lack some important features that third-party calendars provide.
While Apple's iPad Calendar can sync pretty nicely with Exchange, it leaves a lot to be desired for Google Calendar users. A far better option for Gcal productivity is Readdle Calendars. This $7 app presents multiple calendars beautifully, and includes features for tracking tasks, as well. It syncs quickly to Google Calendar, and it lets you drag and drop events smoothly to reschedule on the fly.
On Honeycomb, a free app called Jorte offers the most compelling set of calendar and task-tracking features I've found in the Android Market, and it syncs with Google Calendar and Google Tasks. Jorte isn't really GTD-optimized, but it is highly adaptable. Despite the fact that Jorte received a poor review from a previous PCWorld reviewer, I strongly suggest it to anyone in the market for a full-featured calendar organizer.
Since Android Honeycomb includes Google's voice-recognition software right out of the box, it's easy to dictate text directly into your software--you don't have to mess with the tablet's on-screen keyboard if you don't want to. iOS has no such feature, but you can add it with a freebie called Dragon Dictation. Longtime followers of voice-recognition software will recognize Dragon as one of the pioneers of PC dictation software, and this app certainly lives up to the legacy. Unfortunately, iOS can't let you use Dragon pervasively throughout the operating system, so you'll have to dictate into Dragon first and then copy and paste the text into the app of your choice.