so you have the affiliate link actually go to another page that you've created, then redirect that page to the affiliate, Alien?
Whether or not the ads on your site are followed or not makes no difference as the mighty "G" can certainly tell if your links are ads or not, especially while they are in the banner form. Quite a few years ago the much quoted and misquoted Mat Cutts, blogged about how banners are easily discounted and also informed all who were concerned enough to look it up that; the main concern was with affiliate sites being thin. If the site exists to offer affiliate banners only and doesn't provide any substantive material then that site might be considered thin and therefore would not rank well without some form of gaming.
If your site is real and offers something of value to the viewer then all the normal methods to gain ranking will help your SERPS. If your site is considered to be a thin affiliate site then you might be better served to employ throw away domains and some black hat techniques. Personally I wouldn't recommend it for obvious reasons but to each his/her own.
As someone who would be considered to be a "super affiliate" and as a 10+ year SEO Director I can tell you from lots of personal experience that not using nofollow on my affiliate codes hasn't hurt any of my top ranking affiliate sites. Don't waste your time with questionable attributes, simply provide value; that’s what will help you rank.
My reading would say that a website should not have too many links (more than 100 per page) and that the value or link-juice passed to linked pages is something like the rank of the originating page divided by the number of outbound links. Therefore, perhaps a no-follow tag would cause Google to not count some of the outbound links and therefore give the links you want to provide juice to a higher value. Why would that matter?? Well, most links on my websites are actually internal links and these links give link-juice to their own internal pages - therefore it would improve the ranking of my website to have better link value.
Does that sound right? So much of these stuff is like Chinese Whispers.
I shouldn't quote Matt Cutts, but I did listen to him talk about this one time..
What I remember, is that he said that every page is going to pass down link juice somewhere, whether to your own internal links, or to the outbound followed links - that link juice is all divided up amongst the total number of links on a page..
and this is when he suggested no following links that you didn't wish to support..
When a website has lots of no follow affiliate links, there is no problem for ranking that web site since that kind of links are mention no follow but your website is do follow.
Now, I know the OP is talking about linking out, but the point here is that the PR is not "saved" and sent elsewhere. PR is not divided among all the followed links; it's divided among all the links, period.
The only time you should use nofollow attribute, IMO, is for the reason it was intended; to deter comment spam when moderation is not an option. Google also wants you to use it when you are selling links.
Since I certainly don't want Google to think I have spammy or sold links on my site, I don't use it.
i will have to look for that video, a live interview at SXSW - i am fairly certain he was not opposed to 'no follows' but this would clearly be a contradiction..
but what about Matt Cutts tweet earlier today about cloaking? does it have any bearing on the type cloaking mentioned in this thread?