Based on initial email here to MacFixIt, most users are pleased with the result, especially if you use the PowerPC version. Even compared to Navigator 3.0 (never mind Communicator), RAM requirements, as listed in the Get Info window of the application are down from a preferred size of 9 Mb to only 4 Mb. The general performance (speed of loading pages and downloading) is generally improved as well.
However, problems and complaints were noted as well:
a. Mail and News gone The single biggest complaint is that the Mail and News features are gone entirely. These were integrated in the older Navigator 3.0.1 (which you can still access from Netscape's ftp archive). Now you will need Communicator to have these features. Actually, if you click on a "mailto" link in Navigator 4.0.3, you will likely find that nothing at all happens. The only apparent solution here is to access Internet Config via Navigator's Identity window in its Preferences. Click on the "Use Internet Config" option and make sure that Internet Config has a mail program (such as Emailer or Eudora) selected as a mailto helper. The Identity window seems to imply that there is a way to access mail without using Internet Config, but - if there is - I could not find how to do it.
b. No more "New Window with this Link" option The second biggest reader comment is that the "New Window With This Link" option, previously available from Navigator's pop-up menu, is now missing in action. Oddly, one reader noted that the resource for this option could still be found (by checking with ResEdit), even though it no longer appears implemented. Also note that, in Mac OS 8, Navigator still does not support the new OS's contextual menus feature.
Update: The Navigator "New window with this frame" command is still present (as least on my Mac). Some users have even reported that the "New Window with this link" option still remains on their Macs (it is not on mine). Still not sure why some have it and some do not. Stay tuned.
c. ObjectSupportLib still installed Navigator still apparently installs ObjectSupportLib 1.2 in Mac OS 8 systems. This is a sure cause of problems. Make sure you delete this file, especially so on PowerPC Macs. (Thanks, Dana Nau and Kurt Kroeger.)
Update: A caveat: as outlined in Troubleshooting Mac OS 8, certain applications, unaware that OSL is no longer needed as a separate extension, may have problems if this file is deleted.
d. Assorted other reports:
One report from Joseph de Dios-Valerio claims that, with the 68K version of Navigator, performance may actually be slower than with previous versions. Macintosh News Network reports installation errors may occur trying to install the 68K version.
Navigator installs the 1.2b3 version of ICeTEe, a third party extension that allows command-clicking of URLs from programs such as SimpleText.
Update Daniel Kapusta notes a bit of good news: "Dragging a text clipping with a URL in it onto a Navigator 4.0.3 window now works as it should. No more 'document contains no data' warnings, as occurred in previous versions."
(Thanks also to Tom Knoff, Tom Cheney, and Mark Tuleweit.)