This is obviously a subjective matter (depends on just how bad your short range vision is), but the N900 is, apart from two or three screens (like manual dialing and incoming call) by default quite unconsiderate. Most dialogs and screens operate with letters that are the roughly the size of the 'N900' mark on the device and it can only be changed in a handful of applications (i.e. the mail client, RSS). To make things worse, variable font size in chat (that includes SMS) is officially wontfix.