Juast to reassure people even further about the theory that competitors can spma-link you until Google slaps you, this was in an email newsletter I received a couple of weeks ago. I cant give a link because there's no post to link to, but this really made sense to me:
Everyone's talking about this at the moment - I wrote about it briefly once already, but it has to be mentioned again.
Real quick: In my mind there is NO doubt that a competitor can drive horrible links to your site en masse and incur on you a penalty in the search engines.
I won't lay out the full argument for you here with documentation and references (perhaps in future I will) but trust me on this... it's real.
It's real BUT...
Not in the way some people expect.
First, you have to realize that people like you and me - who follow the Unstoppable Affiliate, small hidden niche method - don't have much to worry about here.
To attract a competitor with the time or resources to bomb your site with thousands of spam links, you need to be in a market where a LOT of money is being made. Not an "elite" niche that's small and underground.
Little guys don't have enough time for their OWN link building let alone to waste it linking to someone else. It has to be REALLY worth someone's while to bomb you out of first place so they can take it. That doesn't happen overnight, or with any insignifant effort.
Second, your site has to be in a certain position to be subject to bombing. A successful negative SEO attack has to call into question the entirety of your REAL link profile; your REAL age, authority, content, and more. It has to outweigh it.
So if your site is new, doesn't have many links, not much age, authority or content, and all of a sudden you get bombed with 1000 spam links... you might be in trouble.
But think about it... if your site is like the above, who's even FINDING it, let alone attacking it? Not likely, right? Then if your site is up in the rankings nice and high where peopel can see it, after having built up real links, real authority, some age and a tonne of content... it's harder to bomb that site anyway. Someone would have to convince Google that all the existing things that they themselves had rewarded, were no longer relevant or important. It doesn't work that way.
I guess what he is saying is that none of us are big enough to need to worry and if we were big, then we would be too big to have to worry 
).
). That's how it works. Link building, keyword stuffing, etc. was yesterday.
