With e-commerce the obvious winner this past holiday season, it's easy to become overwhelmed by Amazon.com's (NASDAQ:AMZN) heady potential. But like those who drink too much bubbly on New Year's, the bulls will be nursing a hangover afterward for their enthusiasm.

Tippling at the speakeasy
My Foolish chum Rick Munarriz pointedly deconstructed my bearish argument that investors would be better off looking elsewhere for more promising opportunities.

I didn't expect the e-tailer's backers to jump for joy over that analysis, but Rick's concise critique was sharply in tune. I particularly liked his assertion that my conservative method of valuation was off by orders of magnitude because analysts already understate Amazon's potential. Touche!

But even if analysts have been wrong in the past, that doesn't mean they'll be wrong in the future, too.

Rick also shouldn't dismiss the Wal-Mart (NYSE:WMT) threat just because it's always engaging in price battles. The discount king is waging one on Amazon's home turf now, and the $10 price point it initiated on popular hardcover books will force Amazon to eschew profits to maintain share.

E-read me a story ...
I will concede to Rick on one point: Barnes & Noble squandered an opportunity to gain ground by not having enough Nook book readers available this Christmas.

Amazon made a big splash by selling more e-books on Christmas Day than physical books, but there's less in that announcement than it seems. With Kindles (and Nooks) being given as Christmas presents, I'd have been more surprised if people didn't rip off the wrapping paper and immediately head off to download something on it.

Of course, we don't know how many Kindles Amazon actually sells, since the company demurs on releasing those figures.

Yet this is a new, emerging niche, and both Barnes & Noble and Sony (NYSE:SNE) will have plenty of opportunities to make up for lost chances. While Amazon enjoys first-mover advantage here, we also can't forget the pending introduction of an e-reader from Apple (NASDAQ:AAPL).

Taxed to death
Rick also dismisses as old news the potential that cash-strapped states will pursue cash-rich e-tailers with a new Internet tax. Investors putting their heads in the sand alongside him do so at their peril, though. I think the threat is even bigger now.

State tax revenues are scarcer than a Goldman Sachs (NYSE:GS) executive who didn't get a bonus. They dropped almost 18% on an inflation-adjusted basis in the second quarter of 2009, and fell another 11% in the third quarter. In fact, 39 states have budget shortfalls at midyear, thanks to shrinking revenue.

A court decision requiring businesses to have a physical presence in the state before it's subject to sales tax collection has protected Amazon thus far from local politicians, but enterprising tax-and-spend politicians have already stretched the definition of "physical presence" to include the affiliate programs of Amazon and eBay (NASDAQ:EBAY) to extend their reach.

Even with the Amazon Tax in place, Rhode Island is still $220 million in the hole, probably because Amazon killed its affiliate program there. It eliminated it in North Carolina, too, but can it afford to do away with those programs in all 50 states?

A juicy target
Probably not. Amazon is expanding the program by allowing bloggers on Google (NASDAQ:GOOG) to monetize their content by integrating ads into their sites. You can do the same thing with your tweets on Twitter. Amazon looks more and more like low-hanging fruit ripe for the picking, but the lucrativeness of its affiliate efforts suggest that the retailer won't easily be able to walk away from the revenues the program generates.

Reason dictates that Amazon shouldn't have to act like some sort of unpaid tax collector, but reason and politics rarely intersect. When the IRS cometh -- and it will -- Amazon's competitive edge over its rivals will evaporate.

With so many other companies out there not sporting valuations approaching 80 times GAAP earnings or 30 times free cash flow, buying Amazon stock is best left off your list of New Year's resolutions. Wait until the market recovers from its drunken debauchery and prices the risks facing Amazon accordingly.

Wal-Mart is a Motley Fool Inside Value recommendation. Google is a Motley Fool Rule Breakers choice. Apple, Amazon.com, and eBay are Motley Fool Stock Advisor recommendations. Try any of our Foolish newsletter services free for 30 days. Motley Fool Options has recommended a bull call spread on eBay.

Fool contributor Rich Duprey owns shares of Wal-Mart but does not have a financial position in any of the other stocks mentioned in this article. You can see his holdings here. The Motley Fool has a disclosure policy.