Raged, WOW!!! This is great information. Puts my worries to bed about the printheads wearing out too soon. I'm so glad you posted this, it is so helpful. 18 rolls you ran? Musta smelled like a vinyl manufacturing plant in your shop! I guess your machine paid for itself (again).
Yeah, they'll run for a LONG time. The only time I've actually replaced them is when they were damaged due to a head strike. It sometimes actually rips the electrical contact film off. Occasionally the machine will say "replace xxx printhead" (the xxx being the particular color). Once, this happened and I didn't have a spare. I took the printhead out, it looked OK, so I cleaned it with regular water and one of the cloths in the HP cleaning kit. It's been running for months since and has no missing jets. In other words, don't throw it away just because the machine says to.
Another thing, the printhead cleaning kit, when it says it's full - it actually isn't. This is per an HP tech who told me this trick. I had a defective cleaning kit and I needed to print "right now". I called HP and the tech told me that you can get extra life out of a full kit using a little isopropyl alcohol, a rag, and piece of white vinyl, in an emergency. When you take a used cleaning kit out of your machine, you'll see a little white paper sticker on the top, kind of on the left hand side, toward the front of the kit in a shallow depression. This sticker will be covered in black ink. Take your iso and rag and clean the ink off around and on it. You don't have to get all the ink off the sticker itself, but the plastic does need to be clean. Take a small piece of white vinyl and cover the old sticker. Voila. New printhead cleaning kit. The way the machine "knows" it's new is that it looks for white in that spot. Once it registers it as replaced, it dumps black ink on it, so it "knows" it's not new. I wouldn't use it for very long like this, but it's good knowledge for an emergency.
Eventually, you will hear LOUD BANGS from your printer. It will scare the crap out of you. Trust me.
This is because the lubricant on the rails is gone or "wore out". Follow the procedures to re-oil the rails, it's in the maintenance menu. The wipes on the sides of the printheads should be cleaned at the same time, even though the manual doesn't really tell you this. You'll need to turn your printer off. Open the window, reach in and move the carriage to the middle of the platen. On either side are small torx screws that hold a piece of plastic over the wipes. Remove the screws and the plastic pieces. The little fabric wipes are just sitting on there. Pull them out. You'll be amazed how nasty they are. I take them and run them under water until they're relatively clean. You can buy new ones from HP if they're really bad. Once clean, use the oil in the HP kit to saturate them. Replace, replace the plastic bit and screw, then oil the rail. Move the carriage back and forth a couple times. Voila, no more bangs!
If you have any questions, send me a message. I'd wager I've been running the L25500 at least as long, if not longer, than anyone on this board. We started with a beta printer in mid-2008 and got our production model in October 2008. I've pretty much seen it all.
Careful what you wish for. Haha! You are the best, thanks for this information. By the way, I already got that print head replacement message thing, it pops up all the time, but prints look fine. If I do the cleaning thing, will that message pop up til I replace the head? Again, I see no problems with the print now. I'm sure message coming up is due to the flipping head strikes I've had. Again, no profiles given to me at first, I had to figure that all out. However, Josh (Bigfish) gave me profiles when I bought something from him recently and I had no issues with his stuff, what a joy that was! He's really great to get materials from. I could not even tell you for sure what head strike meant a few months ago. It ain't 
, that is the self inflicted one. 
Glad you have a bunch as well, they do surprise you, don't they! By the way, I do love the printer and the software. They won't let me print any money for real yet, haha! But if I ever do.... Hey, I got a cash register for Christmas the year before last and practiced using it with monopoly money. I really did do this! That was fun! Would that work? 
Will post more later as we get it up and running.
