FOLLOW-UP (Clarification) - I have an update I wanted to share in case anyone is having similar problems.
My setup: Macbook Pro, running snow leopard (10.6.3), HP Laserjet 3015 (connected via USB), I've installed the HP Laserjet All-In-One Software (v 5.9.5) that I found here:
http://h20000.www2.hp.com/bizsupport/TechSupport/SoftwareIndex.jsp?lang=en&cc=us &prodNameId=378050&prodTypeId=18972&prodSeriesId=378048&swLang=8&taskId=135&swEn vOID=219
As I mentioned in my prior post I could not reliably print and scan. When the printer was working fine the scanner wasn't. When the scanning function was working fine the print jobs would not print.
I have just discovered the problem (and the fix). When the HP Communications App is running the scanning function works fine. Meaning, when HP Comm is running and I put a document into the document feeder on the laserjet, HP Director launches and from there I can run HP Scan perfectly. If HP Communications is not running then nothing happens when I put a doc into the feeder. To know if this App is running I simply looked at the Activity Monitor. What I also discovered is that when HP Comm is running I cannot print. I send a print job to the printer and it puts the print job into the printer queue but it just sits there. The status says "Waiting for printer to become available". For some reason the HP Communications App will not let the job be sent over to the printer. To get that job to print I just go back to the Activity Monitor, select the HP Communications App from the list and hit "Quit Process" and then "Quit" from the next pop-up. And voila the job gets printed.
When you install the HP Laserjet All-in-one software, it forces HP Communications to launch on startup. For me, I print 99.99% of the time and scan .01%. So to make things easier I had to prevent HP Communications from launching every time I reboot the computer. I did this by going to System Preferences, Accounts, pick my name, click Login Items, and delete HP Communications from the list. Oh, once I did that, the annoying Text Edit box called "HP Communications" no longer pops up when rebooting. Now, whenever I want to scan, I manually launch the HP Communications App (found at [Macintosh HD]>Library>Printers>hp). To make it even easier I just put an Alias to the HP Communications App down in my Dock. Once I'm done scanning I just Quit that process in the Activity Monitor so I can resume normal printing.
It's somewhat of a pain in the butt, however, until HP (or Apple) fixes the bug, at least I can fully utilize the HP Laserjet 3015.