A good portion of the problem seems to come from the fact that people are taking a variaty of positions on what Vancian spellcasting is, and for various reasons therefore I think that people are talking past each other.
For me, if I look at the system and see:
a) A list of spells or powers that produce well defined results.
b) A list of slots, which may or may not be interchangable at some point, which are filled with these powers and which give the spellcaster access to the spells.
c) A refresh rate on the spells such that they can only be used one time each and then don't refresh until some period of time has passed, usually after one in game day. However, the time period in question could be something like 'once you leave the dungeon', 'once you have rested completely', or 'once every X hours' (which on a technical basis was true of low level AD&D spells, though this rule was often ignored), and it would still for my purposes be Vancian.
Now, a system could be more or less strictly Vancian depending on how many additional features it has similar to the D&D Wizard (spells are written in old tomes, preselection and preparation of the powers, use of incantations, etc.) and its inspiration in the source material, but for my purposes anything like the above makes me think 'Vancian' when I see it.
So it confuses the heck out of me when people talk about how they hate Vancian, and then go on to talk about how they are ok with the mechanics for Sorcerers or Magisters or would be happy with a short list of selectable daily powers, because all of those to me are basically Vancian variants which can quite happily and easily coexist alongside the traditional D&D Wizard and indeed largely share mechanics.
When I think of 'non-Vancian', I'm thinking of something like the following:
a) An 'at will' resourceless system where players buy spell powers at character creation time in a manner similar to a fighter buys combat feats, and thereafter may use at will any spell that they have learned whenever they want. This might be similar to M&M or HERO without some of the more advanced options that let you broadly simulate anything. 4e without daily or encounter powers at all, as some have said they wished for, would also be an example.
b) A 'mana point' system similar to GURPS or the 3.5 Psion where you buy powers at character creation time, and then have a single shared resource that you must spend to activate your powers.
c) A free form system (also called BSing), where you buy access to spell seeds of various sorts during character creation, and then during the game you narrate the effect you wish to create and the DM adjudicates it based on how powerful he thinks the effect is, how creative he finds it, and other aspects of your narration.
d) Some combination of the above. For example, EnWorld's Elements of Magic uses both spell seeds to create spells with specific effects and mana points to limit the player's access to those spells.
So how many of the "D&D lovers who hate Vancian Magic", really mean, "I hate the D&D wizard, but are fine with something like the Sorcerer", and how many of them hate it in any form and prefer something that is definately non-Vancian.