PROBLEM SOLVED YEAH. It was a server-side issue relating to Nagle's algorithm. I fixed the problem by setting an additional socket option. Now I'm getting awesomely prompt position updates and very smooth movement. It's worth noting that there is usually a hiccup at the beginning but then everything is smooth sailing.
Code:
socketDataHandler running at 1242238803.234
client.movePlayer running at 1242238803234
client.movePlayer running at 1242238803250
client.movePlayer running at 1242238803250
client.movePlayer running at 1242238803250
client.movePlayer running at 1242238803250
client.movePlayer running at 1242238803250
client.movePlayer running at 1242238803250
client.movePlayer running at 1242238803265
socketDataHandler running at 1242238803.312
client.movePlayer running at 1242238803312
socketDataHandler running at 1242238803.343
client.movePlayer running at 1242238803343
socketDataHandler running at 1242238803.375
client.movePlayer running at 1242238803375
socketDataHandler running at 1242238803.406
client.movePlayer running at 1242238803406
socketDataHandler running at 1242238803.437
client.movePlayer running at 1242238803453
socketDataHandler running at 1242238803.468
client.movePlayer running at 1242238803484
socketDataHandler running at 1242238803.5
client.movePlayer running at 1242238803515
socketDataHandler running at 1242238803.546
client.movePlayer running at 1242238803546
socketDataHandler running at 1242238803.578
client.movePlayer running at 1242238803578
BAng! position updates every 30 milliseconds or so. Pretty awesome.