I am having the exact same problem. Not when recording, but during playback. Have seen it on multiple computers, with different drivers. Playback just "stops" -- like it gets stuck for about a second or two, and then continues. Makes it impossible to continue with the SW. Being a computer guy, it really looks like it is loading up the disk read buffer and not returning to the disk until it runs out completely. CPU usage is nil and disk usage is also nil -- until the skip in the audio and then a small activity.
Has happened on both 32 bit and 64 bit Win computers... both WinXP and Win7. Good thing I did not pay for the SW yet, and now looking into Sonar and Cubase. Ableton for me is like writing left handed -- one can do it, but totally different than the others.
If anyone has an idea -- please let me know.
Tks.
EDIT... this is when there are 4-5 tracks in playback... plain audio, no other processing (never could get that far, due to problems)