The following pertains specifically to the update from version 4 to version 5, but I think many of the points are relevant to purchasers of the full version.
I bought version 3 and and the update to 4, with which I have been relatively satisfied, given the known limits of machine translation. Version 5, however, has proven a major disappointment.
(1) There is no English user interface!!! While it's relatively clear that anyone using the program probably knows at least some German, there are weird people - like me - who have an English operating system and prefer (not for reasons of language chauvinism, but old habits die hard) to use their programs with English menus. This option was available in versions 3 and 4. In five, it's gone with the wind. :-(
(2) Like many new programs, version 5 uses the TCP/IP (internet protocol) for parts of the program (including the various MS application plug-ins) to communicate with each other. This creates a "problem" for people using firewalls, which - as they should - ring an alarm bell that the program is trying to contact the Internet, even though it actually isn't. Langenscheidt support offers an email that helps in solving this problem by giving instructions on how to configure your firewall.
(3) In the interface of the older versions, the user could "watch" the progress of both the original and the target files as the program translated the text (even book chapters of 30 - 40 pages) sentence by sentence. This happens relatively quickly, but I used to sit and take notes of specific points that caught my eye, and I would deal with those sections of the target file immediately.
Now one sees only a little "blue bar" that moves left-right-left on the screen; the "translation process" takes place 100% behind the scenes.
(4) In contrast to version 4, my brief test revealed that the program cannot handle texts with footnotes: the output file is a jumble that - at least in my work - is absolutely useless.
I'm translating a relatively long academic text (German to English), and every chapter has a hundred or so footnotes. The original files to be translated (.rtf format) have been professionally prepared and use a complex font (Beyrut Times Roman) that involves lots of special symbols for the transcription of words written in Arabic script (Arabic, Persian, etc.). Of course this script has to be installed on your computer.
Anyway, the output (target) files from version 4 were perfectly formatted renderings of the original (footnote order and numbering correct, special symbols, etc. OK). With version 5, however, I got a mess, where the footnotes were integrated into the text without numbers, and, after about 20 lines of text, the rest of the file was inexplicably underlined. Though given the uselessness of the entire file, the underlining was actually no big deal, it was just another indication of the problems I experienced with version 5.
Of course, as they say, "... your mileage may vary depending on your driving habits ..."
(5) A relativley detailed review of the product (the full version, not just the update) can be found in the German computer magazine c't 21/03, page 174.
Summary: I'm really sorry to have to say that my experience with the update from Version 4.0 -> 5.0 of the Langenscheidt T1 Professional English - German has been anything but "happy".