The banding problem?
When you print, the area where the ink cartridge hit looks like a "band". If you've ever printed large solid areas on an ImageWriter and know of the little rectangular bands you get, this is the problem the 740 would develop. The trouble is that these bands would frequently get out of alignment (unlike on an ImageWriter). It was also noticeable when printing in color--there would be slight gaps between color bands (you'd see a line of yellow, for example, in the middle of your photograph).
Before I got my 740 I had been using a DeskJet 722c on an IBM as my photo printer. The 722c made the user align the print heads every time a new cartridge was installed. This was done by matching one of several patterns printed out with an image on screen. The 740 never made me do that and I'm willing to bet that it got out of sync because of that.
The HP DeskJet 710/720 series was another printer that was extremely popular in the late 1990s. However, it had a few shortcomings of its own--it was parallel only and was Windows only (it did not work on MS-DOS and I could not get it to work this past year when I tried using it as a printer for WordPerfect 5.1). I actually think the 722c was a better printer overall than the 740 though; I remember the color balance being better on the 722c plus my 722c doesn't have a band problem despite being two years older.
Inkjets as a whole are, to me, the biggest pain in computing. I don't have any set up right now and only occasionally get my old Canon i450 out to print photos (usually I only do this at Christmas so I can get a few cards generated for the few people I know who don't use e-mail). The cost of ink and the rate at which these printers consume it made a laser printer the obvious choice for someone whose needs are mostly black and white text. I still have my old 722c and 740, yet both are just sitting around (they are my only parallel printers though so I keep them around for whenever I get my IBM out or if either the i450 or the LaserJet breaks).