How to walk a webgraph?

[Dennis Kubes]

Does anybody know how to efficiently (non-exponentially) walk a web 
graph to detect cycles.  This would be very useful in identifying spammy 
webpage and tight knit communities.

I have a program that I will be releasing soon that does the detection 
through converting a webgraph into a tree and walking the tree nodes, 
but it is exponential in terms of intermediate map reduce output and 
computation.

Dennis