Not very good in my experience. I've worked repairing printers for the past few years so I've been able to get a good look at quality of build on these things. This definitely has put me off of telling anyone to get a Brother machine ever again. For the money it seems to me like buying a refurbished midline HP laser is a good way to go. Something in the 4000/4200 series. Also, I don't get why people insist on Lexmark/Dell machines. Messy as hell, problematic, badly fitting peripherals and pain in the ass maintenance.
I haven't work on as many printers as MayonakaHa, but I have bought 6 Brother laser printers over the last 5 years for myself and my parents, and have successfully weaned them off of buying crappy inkjets. The Brother HL1440 printer I bought in 2003 is still at my parents house on the original cartridge cranking out great print quality. YMMV, but my Brothers are great.
Doubt is a pain too lonely to know that faith is his twin brother. - Kahlil Gibran