I just wanted to post an example of something I was a little afraid of getting penalized for: Say you have a site that sells DVDs - and one page has a listing of 25 DVDs on it. Each one has a link next to it that says "Buy this DVD". Say the density of the phrase "buy this dvd" is at a density of 30%. Do you get penalized for that? It's obviously not an attempt to be #1 for that search phrase. Alternately, if you have a traditional site directory/site map with links next to each category that say "Go there", will you get penalized for listing "Go there" 40 times on the page? I just want to know how subjective this is. If the above example will penalize you, is there any way to omit search engines from spidering that link, and even so, do you still get a penalty for it?
If go there has nothing to do with what your website is about, then no you wouldn't be penalized. But if you sell DVD's and every button says "buy dvd" - you probably wouldn't be penalized but its not good either. Google would really rather see each one of those ALT tags more specific to the product. For instance, if you could get each ALT tag for each product to display the product name - its more specific, better for a bot, and better for the end user. Does that make sense?
This is a very good example of how to get busted. I would use an image to do this. 30% is pushing it. If this is a dynamic site that will have content being added over time, then you will get busted. 25 DVD is one thing 100+ isn't. But then comes the arguement of "add to shopping cart" that is done all the time. Google just ignors this. Just go slow on this, motive is what a manual review goes on.
If your site is selling DVDs, I don't see why a Buy This DVD link would hurt you too much. But, maybe you could use a Buy DVD graphic button link with an ALT tag of the name of the DVD instead of a text link, if you're worried about over saturation.
I think you may sell more DVDs with "buy this DVD" than if you put "buy this". So factor that into the equation. Then again, an image may be your best conversion. Then again, images don't always load. It sounds like you are using a database. So, I'd probably go with "Buy Terminator 2" or whatever your DVD title is. That would be the best method in my opinion. Brandon