Well, I think when abfan123 says "standard mode", he means the "standard way that Avant/IE has always previously run", which is fine, except that it will start to get really confusing when IE8 is released.

That's because it must be differentiated from the official IE8 terminology of "IE7 compliant mode" (the way Avant/IE has always previously run in IE7 and earlier) and "IE8 Standards Mode" (the way IE8 follows W3C internet standards for external websites). I personally think it is really bad to use the word "standard" when referring to IE7 and earlier because it does not follow W3C standardS, and also will _NOT_ be the default when upgrading to IE8 (IE8 Standards Mode [following W3C standardS] is the IE8 default for external websites).
As well, I suggest to definitely try _NOT_ to run Avant in the previous/IE7 mode, but rather to run it in IE8 mode as much as possible. Then you will see which websites work according to W3C standards and which do not, and as users, we can notify the website admins of non-compliant websites to fix their websites to be W3C compliant.
Of course, that is why IE7-mode is still available in IE8. Until broken/non-compliant websites are fixed, or if problems are encountered in daily use (eg. your GMail problem in Windows 7) then you can switch to IE7 as a workaround (and notify the problem website admins). But IE7-mode is definitely the workaround mode, and you should switch back to IE8 mode when you are finished with the problem website.