: 
: What are the current products available to upgrade the resolution?
: Which ones support postscript?
: 
: Any experiences with them, either good or bad?
: 
: Is the quality difference really noticable?
: 
: I'm planning on producing camera ready copy of homes.  Will the higher
: resolution be noticed for these?
: 
If you are talking about laser jet 4 then I believe it has to be postscript.
I don't see any advantage to using PCL when you have a peice of hardware
plugged into the LJ4 that is doing the work and it can support any language
that is suited for the job.  Besides I don't think PCL is even capable of
handling 1200 dpi specifications.  I only have experience with the Laser
Master Winjet 1200 which brings the LJ4 up to 1200 dpi and it uses postscript.
It also has a fast print mode which is not postscript, and it is at a lower
resolution (600dpi I think), but it is FAST!!!!  This particular product
uses your host processor to process the postscript, so even with a decent
PC you know it's going to be slow i.e. slow compared to a high-end workstation
processed PS.

The quality difference is very noticable and is almost worth the wait (for
the PS processing) - I'm rather impatient.

We were using it for B&W camera images (RS-170).  The gray scale image was
accepted by MS Word and handed to the Winjet PS printer driver which converts
the image into postscript and then hands it off to the Winjets postscript
processor.  The postscript is rendered into RAM (lots of it) and when it
is done it shoots it directly to the printer.  The PS processor can also
accept PS files created from other sources including DOS applications, but
Windows has to be running at the time of printing.  The PS processor is
responsible for the halftoning and I'd say it does a pretty good job.  Our
camera images came out very good in my opinion.  (not as good as Laser Master's
demo though).

I don't know how many other similar products are out there but I would be
surprised if there are several.