ZEB B  Spend some time looking at: http://textware.com/overview/overviewpage.htm

The bottom line is that Instant Text does not depend on learning abbreviations or on typing the starts of words. As an example not mentioned on the web page, I use a shorthand based on NoteScript by Lawrence Hawkins (at amazon.com). There are a few specialized abbreviations, but most of the savings comes from elimination of vowels ( e.g. "elmntn of vwls"). Instant Text learns a system like this with very little training.  
(Version 4.2)

ZEB B  None of these programs holds a candle to Instant Text by Textware in Windows. For a serious typist, Instant Text is reason enough to stay with a PC or to run Windows in a virtual machine.

Wanted: a dev to partner with Textware and port Instant Text to the Mac.   
(Version 4.2)

MUUSER  Most recent version posts only a blank screen when the pref panel is selected (Typeit4me 4.2 purported to work with Snow Leopard but no go here). No apparent solution in sight (none offered in response to two email reports of this problem). Reinstalling 4.1.2 (as per prior comment) corrects the problem -- but that version is not available in the links on the download page on the developer's site.  
(Version 4.1.3)

SLOB  Developer - get your versions right. The download results in version 4.1.2. So the 'upgrade' results in a hang.  
(Version 4.1.3)

WRITESTUFF  I've used this for years and just can't do without it. Yes it can be a little slow, but with so many features I can accept a few drawbacks. User names, passwords addresses, etc., all at a click of the mouse. What more do you need?

Now there is the auto spelling, with the Mac voice 'Whisper' to tell you when you've got it wrong and key clicks for odd words.

Marvellous and thank you.  
(Version 4.0.3)

MMUECK  I've been using this product for over a year and have been at the developer for most of that time to deal with an infuriating issue with the text expansions. I've found the developer to be much more interested in adding features than fixing issues. On the average, about once in every couple dozen expansions (I have a library of over 2500 expansions) the expanded text gets all mangled e.g. the result is some combination of the abbreviation and the final text, or it fails to include the trigger character, or the expansion occurs in the middle of the following word etc. It's true you can really blast along typing at higher speeds (although I'm just a medium speed 4 finger peck and shoot typist), but I'm sure spending a lot of time having to meticulously proof read the result of my typing to fix all the expansion mangling. I also own Typinator and TextExpander and they don't have this problem. The ONLY reason I've been putting up with TypeIt4Me is because it does single-character expansions and the competition didn't. I've been urging the developer of Typinator to implement this feature and he's finally released a version that does it! However, his implementation has a couple killer limitations that must to be addressed before I jump ship, but he's getting there.  
(Version 4.0.2)

TUNT  I noticed a little bug in 4.0.1, starting in Off-Mode, and Riccardo fixed it in a day. TypeIt4Me works great and saves a lot of time!  
(Version 4.0.2)

SLOB  Works ok on an intel though the installation was slightly clunky (T4me not reading my default file until it was pointed to it) - but on my g4 pbook.. oops, blank pref screen even after machine restart. Lucky the previous version was backed up which still works fine. So be careful with this, looks like late beta.  
(Version 3.2)

MACAL  Bought this a LONG time ago and never really used it so almost forgot it. Then, on a whim, I dowwnloaded the latest version. WOW!

Much, much better intergartion and performance than I remembered. Is now a 'must' when installing/reinstalling.  
(Version 3.0.1)

WILMA  A fantastic and indespensible program! I use TypeIt4Me all day, every day, in both Classic and OS X. Unlike Spell Catcher (which I use like a dictionary for looking up words), TypeIt4Me shares the SAME shortcuts file for Classic and OS X -- so you can instantly change, add, or delete a shortcut from either interface, and it updates both!

TypeIt4Me is fantastic for:

+ Correcting commonly mispelled words (such as "teh" for "the")

+ Email signatures and tag lines, phone numbers, addresses, etc.

+ Shortcutting long or difficult-to-spell words, phrases, and names

+ Shortcutting common phrases and names that you type a lot

It takes only seconds to add, modify, or delete a shortcut, which makes TypeIt4Me very handy for typing a document with a bunch of repetitions of some name or phrase, then deleting the shortcut afterwards.

I use this program hundreds to thousands of times per day. It has speeded up my typing, reduced my spelling errors, and made my life a lot easier.  
(Version 3.0b31)