Here is a good video from Sports Science on putting speed and lip outs.
Pretty much all of this is right in line with Geoff Mangum's (www.puttingzone.com) research on the subject.
I know we have discussed uphill putts being easier to make and the video indicates that it may not be the case as the downhill putts gravitate more towards the cup. From my reading of Mangum's work, he likes to point out that *may* be a reason as to why downhill putts *may* be easier to make.
However, the research done from Mark Sweeney of AimPoint and David Orr (www.orrgolf.com) shows that golfers make a higher percentage of uphill putts than downhill putts for all levels. To me, that is the final decider.
Perhaps it can explain why there are some exceptions to the rule. I remember Ben Crenshaw saying that he preferred downhill versus uphill putts. Whether he actually made more downhill than uphill putts is up for debate.
Either way, I think this is a required viewing for a better understanding of putting.