I have been using a 5GB Toshiba PCMICA Hard Drive for about a month now. I have not had any problems whatsoever and it works great. No heat problems or skipping. It holds lots of music and provides great quality sound. I bought the Hard Drive on Ebay for $50 but it is also for sale at
www.tigerdirect.com for $80. Cheaper than an Flash Memory card. Only downside it takes about 2-3 seconds longer for the music to play once you turn the car on at start up, if that is a problem for you.