Interesting article.
http://news.bbc.co.uk/sport1/hi/football/9379989.stm
Since the start of the 2007/8 season, 15 opposition players have been sent off against Manchester United at Old Trafford, while only three home players have been dismissed.
And as far as penalties go, opposition teams have given away eight at Old Trafford since 2007, while United have conceded only two.
Just to show I'm not totally biased -
Six Chelsea players have been sent off at Stamford Bridge since 2007, twice the number of opposition players who have received red cards, while the Blues have won 18 penalties, six times the number of spot-kicks won by visiting teams.