John, I've been using the Toshiba microdrive for a couple of years. It does produce additional drain on the battery and I've seen suggestions that you take out the drive when you're not using it. Since my drive has been around for a couple of years, I really can't speak to any of the more recent drives.
Also, in some cases, the response of the microdrive is a bit slower than a standard pcmcia or flash card, so in some situations this might also be a consideration. The Toshiba drives are apparently rather hard to find now, so you'll probably be getting something more current and hopefully a bit more energy efficient. Given the amount of extra space you get with these drives though, I still think the additional battery drain is worth getting the drive. Don
