I made this sample program that demonstrates that Allegro has some serious input delay, I tested it on Windows (no other OS nearby now, sorry 
)
You can play "normally" and you will notice that the controls are not tight as they should (for a action game at least), but you can REALLY see the effect if you just press arrow keys in random directions as fast as you can (like if you was making a fighting game input), and then just watch the screen, the longer you made your "combo", the longer the ship will move on its own.
EDIT: Fixed a bug in the example code that Elias noticed.
1//libraries
2#include <stdio.h>
3#include <allegro5/allegro.h>
4#include <allegro5/allegro_primitives.h>
5
6//project headers
7#include "gamelogic.h"
8
9const int PLAYFIELD_W = 1280;
10const int PLAYFIELD_H = 720;
11#define UPDATE_TIME 1.0/125 //1 second divided by 125 frames per second, this is to guarantee a round milisecond speed
12
13ALLEGRO_KEYBOARD_STATE keyboardState;
14
15int main()
16{
17 ALLEGRO_MONITOR_INFO monitorInformation;
18 ALLEGRO_DISPLAY *display;
19 ALLEGRO_EVENT_QUEUE *events;
20 ALLEGRO_TIMER *updateTimer;
21 int screenWidth;
22 int screenHeight;
23 int counter;
24
25 ////////////////////////////
26 //Setup phase starts here //
27 ////////////////////////////
28 if(!al_init())
29 {
30 fprintf(stderr, "Failure loading Allegro\n"); //should not happen, but who knows...
31 return 1;
32 }
33
34 //now we create our display
35 counter = 0;
36 while(al_get_monitor_info(counter, &monitorInformation)) //this function returns false when it fails
37 {
38 if(monitorInformation.x1 == 0 && monitorInformation.x2 != 0) break; //we found what we wanted
39 ++counter;
40 }
41
42 screenWidth = monitorInformation.x2 - monitorInformation.x1;
43 screenHeight = monitorInformation.y2 - monitorInformation.y1;
44
45 al_set_new_display_flags(ALLEGRO_FULLSCREEN);
46 al_set_new_display_option(ALLEGRO_VSYNC, 1, ALLEGRO_SUGGEST);
47 display = al_create_display(screenWidth, screenHeight);
48 if(!display)
49 {
50 fprintf(stderr, "Failure setting up the display\n");
51 return 2;
52 }
53
54 if(!al_install_keyboard())
55 {
56 fprintf(stderr, "Failure installing keyboard\n");
57 al_destroy_display(display);
58 return 3;
59 }
60
61 if(!al_init_primitives_addon())
62 {
63 fprintf(stderr, "Failure loading primitives addon\n");
64 al_destroy_display(display);
65 return 4;
66 }
67
68 updateTimer = al_create_timer(UPDATE_TIME);
69
70 events = al_create_event_queue();
71 if(!events)
72 {
73 fprintf(stderr, "Somehow there was a failure creating a event queue, this really should not have happened\n");
74 al_destroy_display(display);
75 return 5;
76 }
77
78 al_register_event_source(events, al_get_display_event_source(display));
79 al_register_event_source(events, al_get_timer_event_source(updateTimer));
80
81 ///////////////////////////
82 //Setup phase ended here //
83 ///////////////////////////
84
85 al_start_timer(updateTimer);
86
87 double playerX = 20.0;
88 double playerY = (double)PLAYFIELD_H/2.0;
89
90 bool redraw = false;
91
92 while(true)
93 {
94 static ALLEGRO_EVENT event;
95 al_wait_for_event(events, &event);
96
97 if(event.type == ALLEGRO_EVENT_TIMER)
98 {
99 //updateGame();
100 al_get_keyboard_state(&keyboardState);
101 if(al_key_down(&keyboardState, ALLEGRO_KEY_DOWN))
102 {
103 playerY+=10;
104 }
105 if(al_key_down(&keyboardState, ALLEGRO_KEY_UP))
106 {
107 playerY+=-10;
108 }
109 if(al_key_down(&keyboardState, ALLEGRO_KEY_LEFT))
110 {
111 playerX+=-10;
112 }
113 if(al_key_down(&keyboardState, ALLEGRO_KEY_RIGHT))
114 {
115 playerX+=10;
116 }
117 redraw = true;
118 }
119 else if(event.type == ALLEGRO_EVENT_DISPLAY_CLOSE)
120 {
121 break;
122 }
123
124 if(redraw && al_is_event_queue_empty(events))
125 {
126 redraw = false;
127 al_clear_to_color(al_map_rgb(0,0,0));
128 al_draw_filled_triangle(playerX-10, playerY-10, playerX+10, playerY, playerX-10, playerY+10, al_map_rgb(255, 255, 255));
129 al_flip_display();
130 }
131 }
132
133
134 printf("hello world!\n");
135
136
137 ///////////////////////////////
138 // Cleanup phase starts here //
139 ///////////////////////////////
140 al_destroy_timer(updateTimer);
141 al_destroy_event_queue(events);
142 al_destroy_display(display);
143 return 0;
144}
]]>
