I have used the C544dn for about 3 years now and it replaced an ancient Xerox solid ink unit which lasted 6 years! So far the Lexmark has proven very reliable and economical on toner and spares.
The print quality is very good, it's fast enough for my needs and the Rewards scheme for toner return is really useful. It is a little noisy when working, but not obtrusive.
I only have two gripes really:
The toner is very expensive compared to other brands and compatibles are not available. That said, the extra high yield cartridges are the best value and especially when Printerland have a sale on!
The other beef is the output tray gets bunched up after 20 pages and this is annoying when printing a long document, particularly when in duplex. All in all - 4 stars!