I have just switched from Wireless to homeplug. My issues were two fold and I think only linked to Vista.
1) I had to rely on the the native vista driver, which meant that every minute I was disconnected whilst it looked for a better signal. I could get round this by switching the zero configuration off through the command prompt or using Vista Anti Lag, but it was a pain.
2) The location of my router and my PC was such that although I got what looked like a good signal, it was in fact rubbish. This meant sudden phases of lag and mad pings in games.
I switched to homeplug, it took about five minutes to do and I am a happy bunny.