The sound quality isn't great with these headphones (e.g. the sound quality on the headphones provided with my iPod Touch is far better), and the microphone sounds a little muffled. Also one of the earpieces rattles slightly. Having said all that, I've not heard many complimentary reviews about the original Apple iPhone headset which is retailing at around £19 (I paid £7.99 for these inc P&P), so actually I think these represent good value. I only use them for VOIP calls via Fring and for fun applications like Midomi, and they are fine for that.
If you want good quality, you should probably opt for the premium in-ear headphones and mic set, but you will pay 5-6 times what I paid for these.