one measure at a time works for me too. If it's a tough solo, even one note at a time just to make sure it's right. I used to wear out cassettes this way but now there are great tools, like Transcribe!, which lets you slow down a solo to 20% while staying in key. If you start with a high quality file, like a WAV, then you get good quality slow-plays. I used this to break down the Van Halen solo for the "You Really Got Me" lesson.