It definitely depends on how you plan to advertise. If you mean Adwords, YPN, etc... Your $90 ad would be next to someone else's $97 or $102 ad.
You can still get full $97 referrals with the standard referral link, even though it's not as easy as it used to be.
If you're just putting it on a site or two, then I guess it would depend what kind of traffic you get and what type of site it is.
If it's a community-type site where others can participate/post, someone would quickly point out that a $90 code isn't the best one out there.
If it's a helpful site, you could give people an option, basically giving them the chance to donate $7 to your site if they found it useful. Like my sig... more people have used the $96 one than the $97.
Some will opt to help you out, while others will take the full $97. You might not make anything on the $97, but on the other hand, the guy that takes the $97 could end up referring a ton of people--so it might not be worth it to lose those people by only offering one.
Actually, people still do. Yes, it pretty much just waives the setup fee -- but plenty of people have signed up for that plan... and paid the setup fee before there were promo codes.
Save up to $96 at Dreamhost with 96DOLLARSOFF promo code (I get $1).
Or save $97 with TAKESEILERSCASH.