Thanks James. yeah, I think in order to reduce my exposure, I'd have had to go to ISO 6400 and despite the 7D reportedly handling that quite well, I just don't like it. I suppose I should have tried it. You'll certainly see star movement even with 30 seconds but if you're at the very short end of the lens, it shouldn't be too apparent. I'm no expert but I imagine shooting the same scene on a full frame camera would also reduce the apparentness of star trailing (at least for me as I was shooting on a crop)
This is a single exposure too. I believe stacking multiple images is a good way of going about shooting the night sky. I know I've used that method for star trails in the past but I know people use stacking for star fields too.