Taken from The Straight Dope
Mainly to continue the tradition of making English as incomprehensible as possible, thereby keeping the spelling bee industry in business. (Believe me, there's millions in it.) Colonel comes from Old Italian colonello, commander of a column of troops, which in turn derives from colonna, column. It wasn't always spelled the Italian way, though. Four hundred years ago English followed the Spanish practice and spelled the word "coronel," sensibly pronounced the way it looked. Eventually this was corrupted to ker-nel, still not bad considering we're talking about the British, who pronounce "Featheringstonehaugh" "Fanshaw."
But it couldn't last. Some nameless busybody decided coronel ought to be spelled "colonel" to better reflect its Italian origin, doubtless out of the same misplaced love of precision that gave us 16-1/2 feet to the rod and 27 and 11/32 grains to the dram. It's just the Anglo-Saxon way, I guess. How these people conquered an empire I'll never know. -- CECIL ADAMS
Another thing that bugs me is when people pernounce "gif", "jif". JIF is a brand of peanut butter! GIF stands for Graphic Interchange Format, a bit-mapped graphics file format used by the World Wide Web. GIF supports color and various resolutions. It also includes data compression, but because it is limited to 256 colors, it is more effective for scanned images such as illustrations rather than color photos. If you pernounce "gif, "jif", then do you pernounce "gift", "jift"? C'mon people. Also, in case you didn't know already JPEG stands for Joint Photographic Experts Group.