Certainly 'Similar Pages' has been transformed post-Allegra.
Instead of thousands, only 31 are now listed next to our No. 1 site in the serps.
Also, the sites listed as 'similar' seem to be picked from a much broader definition of similar.
Say, for example a site about dogs...
Thousands of Similar Pages detailing different dog breeds, dog feeding and dog care
Only 31 SPs: covering dog breeds, cats, ferrets, budgies, and dog days
In my opinion, pre Allegra was better both for webmasters and searchers.
MSN must be delighted, we're certainly seeing our visitors arriving from MSN search rising daily. Was 2% last month, now 10%.