Sliding keyboards work amazingly well. Given a moderately practiced user typing English text and reasonably fast hardware, I suspect that a "typing" speed could be achieved that would be nearly competitive with a full-sized mechanical keyboard.
Android provides at least two sliding keyboards so far, and here are their relative strengths and weaknesses.
- Fastest for raw text, though this difference may only be noticeable on lower-end hardware.
- Supports custom macros, called "shortcuts" that allow for arbitrary letter combinations to expand to any arbitrary text.
- Does not require swiping over the apostrophe for contractions.
- Switching to the symbols keyboard then sometimes requires scrolling through rows of symbols, and automatically switches back to the regular keyboard after typing each symbol (which can be frustrating when typing pairs of parentheses or brackets), unless "pinned", which requires an additional keystroke.
- Symbols and accented letter keys are visible and can be found easily (if not quickly) when scrolling through keyboard.
- Has built-in voice input support. This is mostly for Android 1.x devices that do not already have this support.
- Has built-in Graffiti (Palm-style block-letter recognition) support.
- Limited paged-horizontal display of alternative word matches.
- Irritatingly disables the shift key after the first letter of a word is typed.
- More than twenty languages supported.
- Always includes a return key.
- Unique keys: ¬ …
- Larger keys.
- Much faster support for capitalization by swiping a letter up above the keyboard, then to the next letter. This makes typing "I" in particular a much faster upward flick than the more cumbersome [Shift], [i].
- Much faster support for symbols (by long-pressing a letter for common symbols, or switching to the symbols keyboard for a more comprehensive selection).
- Extended symbols and accented characters are not visible until long-long-pressing a key (in either symbol or regular keyboard mode). Location of symbols can be difficult to find and remember until the mnemonically understood.
- Numeric keyboard.
- Limited paged-vertical display of alternative word matches.
- Contractions require swiping the apostrophe.
- Swiping period/exclamation/question to space quickly ends a sentence.
- Variable speed-vs.-accuracy slider setting.
- Extra hidden keyboard for powerful cursor, selection, and clipboard control.
- Three languages supported (English, French, Spanish).
- Return key is often irritatingly replaced with "Done" key.
- Unique keys: ¿ ¡ „ ð · þ ¶ ª æ œ ß