Just a quick update on my Lexmark C544dn: Buy this beastie more memory! It's not like it's obnoxiously slow with the standard amount of memory, but adding more memory is really cheap and it speeds things up tremendously in a couple of situations. First, if you tend to print n-up pages (multiple page images on a single side of paper), and second, if you print double-sided with anything beyond simple text (web pages are a good example). At least, those are the cases I found where the printer bogs down a bit.
I bought a 512MB module directly from Crucial, and with tax and shipping it was only $35. It's simple to add since you only need to unscrew the back panel (six Phillips screws, not four like is shown in the manual) to expose the printer's empty memory slot. After adding the extra memory I can print a document 2-up, double-sided, and the printer runs at the print engine's speed—no more long pauses between sides or sheets.
One other observation after having used the printer for a little longer: some reviewers dinged it because double-sided printing slows down the overall output speed considerably when compared with some other printers in its class. I figured that I wouldn't use the double-sided functionality that often, so I didn't let that drawback weigh very heavily in my decision-making process. Now that I have the printer, though, double-sided printing is so easy to do that I find myself making use of it much more than I expected. Still, the performance hit isn't bothersome to me and the added memory speeds it up a bit, too.
Overall I'm still quite happy with this printer.