I'd say it's down to the quality of links - If all of the sudden you get 500 links from spammy/new sites then this looks suspect, hoever if you were to get 500 links in a day from trusted sites then the Se's would surly see that you have just created a marketing buzz. Also - Could humans be involved? i.e - if a site has xxx links per day, it would be easy to look to see what sites/quality are linking to them and have a human make a decision... Just build links naturally, organically and you'll be fine
well, If do in a short time, like just for 1 day. That would be possible. It looks spammy when you got lots of backlinks just for a day. Just link to related site and create good content.