I'm certainly not knocking all aftermarket wheels...what I'm referring to when I say "replica" is not just any aftermarket wheel that will fit a BMW, but wheels that are actually listed as "BMW Replica" or "BMW Style" wheels that are intended to clone the OEMs
Here is an example:
http://sfbay.craigslist.org/sby/pts/853657849.html
These wheels are copies of the OEMs, but do not carry the mfr numbering on the back of the spokes and rim. Some are fine I'm sure but the quality will vary.