We keep ours for the 911 feature. Cells, VoIP, etc simply are not as reliable in the event of an emergency. To me, the small amount it costs (and ours is part of a bundle, including phone, internet and cable...if we drop the landline we save hardly anything...like $5) is worth it for the peace of mind I have. Also, we retain a phone that is CORDED, rather than have all cordless phones. Cordless phones do not work in a power outage...just as cells and VoIP have limited usefulness in a power outage. Landline corded phones are powered by the phone network itself, and will run for as long as the generators at the central office run...many many days.
Also, for those who live in earthquake country (or hurricane country), as I used to, cell service is easily OVERWHELMED during a natural disaster (or an unnatural one like a terrorist attack). Cells were essentially useless because the design of the network is very different than landlines. Landlines, however, are engineered to handle peak load on peak day...and therefore are much more able to handle the increased volumes during a high demand time like a disaster.
Until these problems are addressed by cells, to me, a cell is a nice convenience but no substitute for a landline phone.