Other than Street Fighter games, and other crappy beat em ups and Neo Geos how many arcade games actually use more than one or two buttons? I am leaning toward using just 2 buttons per player, sort of in a line shape like this.
o o
The first button exactly fits my index finger, and therefore would be perfect for games like Galaga. The 2nd button provides a little more flexibility and shouldn't get in the way.
Am I missing a lot by not going for the standard "eighty-seven" buttons??? I mostly plan on playing classic games, but I may have friends over who want to play some of the newer stuff (Final Fight maybe?).
Any comments welcome, and needed!

Not sure if this post was meant to be sarcastic (and no one else caught it) or not, (given the recent posts on "Are 6 buttons necessary) and "Diamond or square for 4-buttons"
In the hope that this is serious, or could be useful to others, here is some excerpts from a page I am doing on choosing a keyboard encoder, which should help this topic (although it is geared more to modular panels and 4 (or more) player support).
This is basically answering the more general "How many buttons do I need?, How many inputs do I need questions?"
Reality Check
Consider the following when evaluating an Encoder ?
For two-player games, many of the classics used only one button per player (Galaga, Gyruss, Time Pilot, Galaxian, Space Invaders, Mario Bros.). Even more used two buttons per player (Sky Shark, Twin Cobra, Tiger-Heli, (most vertical shooters, for that matter, Double Dragon, Rolling Thunder, and a lot of the horizontal scrollers, etc.) Three button games were somewhat rarer (Gun.Smoke, Missile Command, Blasteroids), but you could spread these inputs over player one and two if required. However, there were a fair number of 4-player 3-button games, and you could play any of these with only two people. There were a few four button games (Defender, Armor Attack, Rip-Off, Star Castle, and some Neo-Geo games, etc.) Of these, only Armor Attack and the Neo-Geo's were two player simultaneous. There were a few 5-button games, notably Asteroids, Asteroids Deluxe, Star Gate and Space Duel, and the early Mortal Kombat series. Of these, only MK and Space Duel were two player simultaneous. Finally, I think only the Street Fighter and Capcom Fighter style games were six-button, simultaneous, but it is a good idea to support this games if there is any chance you (or your friends) might be playing them.
There are many 3-player and 4-player 3-button games. There are no 3-player 4-button games. There is only one 3-player 5-button game "Guardians of the Hood" in MAME as a test driver, and only one 3-player 6-button game "Powerpuff Girls", Status unknown.
There are three 4-player 4-button games - Dungeons & Dragons - Shadow Over Mystera, Dungeons & Dragons - Tower of Doom, and NBA Jam Extreme. There are no 4-player games with more than 4 buttons. Super Street Fighter 2 - Tournament Edition is 4-player but 2 players play at any time and alternate. War: Final Assault is 4-player with 6 buttons and a trigger stick with thumb button (8 buttons) but the game had 4 cabinets networked together, so it should be considered single player when designing a cabinet.
There are no 5-player games, however, I have included them in the considerations below, because it may be possible to play a 6-player game with only 5-players present using some of the encoders.
There is one 6-player 2-button game "Hard Dunk (emulated by Modeler and MAME, but the MAME version is 2-player only), two 6-player 3-button games - X-men and JSR Arcade - Second Chapter and one 6-player 6-button game, Clue (although I think that one may be bogus).
In addition, while these games expect discrete coin inputs, in most cases the P1 Start buttons, etc., while present on the CP, are actually mapped in parallel to the P1B1 buttons, so these can be eliminated when planning a CP.
(To be continued . . . )