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Well, MacConnection has been around for a LONG time, and I used to buy stuff from them all the time in the days of catalog sales. Always was very happy with their service.

I haven't bought anything there recently, but at the very least they're certainly not fly-by-night. BizRate has moderately good reviews of them:

http://www.bizrate.com/ratings_guide/cust_reviews__mid--465.html

...but I noticed that most of the complaints were about mail in rebates. Personally I really hate rebates and go out of my way not to buy products that have them, since it's just shy of a legal scam.
 
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