The rating system is based,i believe,on the chances of the download succeeding,available download slots etc.So far I've not had a 4 star d/l fail.Also the resume on startup feature works a treat too,I was in the middle of a lond download when (due to my fault) a system crash occured,on startup it resumed the download without prompting,lovely.

As for the cpu usage,I've never had any problems with excess usage,and can happily carry on with other programs unhindered.