I also had issues, and it was definitely due to the downloading on the background. At first it was taking extremely long to startup – higher than normal CPU usage, and memory usage slowly climbing. I let it do it’s thing and came back several minutes later to find an unresponsive OS. Memory (including swap) was completely full.
I killed the process, rebooted, and started meteor up again to start with clean resources. Finally didn’t have to wait several minutes to get the “App running at:…” prompt, but saw that there were still downloads in the background. I monitored my resources, CPU usage was steady but unnecessarily high (really… it’s just a download, no?) – and the memory usage was steadily climbing… quickly. Finally after the download finished CPU usage stopped, and now meteor had climbed to almost 2GB of memory… in under a minute, this is over 3x normal usage.
After killing the process yet again, and restarting meteor I found everything was back to normal.