It can be difficult to tell for certain, however Barry has a good checklist:
Quote:
# Is that page indexed in the search engine?
# Does the page have toolbar PageRank?
# Does the page have inbound links?
# Are outgoing links from that page found in a link command at Yahoo from the reciprocating page?
# Does that page rank well for unique text found on the page in the search engine?
I have a look at what backlinks google is showing for my competetors who are optimising for similar keywords and try and get all of the links they have any more. To date I have gained loads of links in yahoo but until the next google backlink update I have no idea how well its working.