Usually, when people exchange links they already have a description written out to go under their website link. Do you think it would be better for your SEO to write a unique description for your partner's website as well a unique description for the link that they post on their site?
If you mean a meta description, I think you should just focus on what the page is about. It should correspond with your title and the content of the page. Forget about what anyone else's website is about, when it's a page on your site. Just put their link on a relevant page on yours and there should be no worries.
Sure, it's always to better to have your link inbetween unique content. As for the anchor text, rotate your main keywords once in a while. It depends on your domain too. If your domain contains is the exact same as your keywords (ex. cheapwebhosting.com), then you can use the same anchor text (ex. cheap web hosting) over and over again without worries
Personally I find it usefull to write at least 5 titles and 5 descriptions and submit them randomly to both directories and reciprocal link submissions. I also like to change them after a week or so as it makes things more unique.
Yes, it's a good idea to have a little uniqueness in your links. If you think of how links were meant to be created: Someone with a site relevant to yours finds a page on your site interesting and wants to share it with his readers, so he writes up a quick blurb on his site and links it to that page on your site. Because it is linked to a deep page on your site, from a deep page on his site, chances are the anchor text and desc. will be unique to the contents of the pages... Therein lies the secret to the perfect link... Charles