I crossed the Eritrea/Ethiopia border the last time it was open--shortly after independence, around 1995. It was fairly confused and chaotic, since different officials on either side had different agendas and ideas about what was required and how things should go.

Assuming the same is true, best bet as always is to be relaxed and friendly to anyone who might have influence, whether uniformed or not. I was saved from several difficult situations by people I'd been talking to casually who then intervened on my behalf. Make sure you've always got entry and exit stamps and any other documentation which might be required--even if you're told you don't need it. It definitely won't hurt to have cards, letters, or just phone numbers of people in positions of possible authority in either government--just the possibility that you might have friends or be connected is enough to grease the wheels. In this respect it'll be just like other African borders, but maybe a bit more so. I hand out my own cards and contact information very freely, and this often prompts people to give me theirs in return.

Take the above with a grain of salt, since it's based on experiences several decades ago. However, the reports I've heard have sounded remarkably similar to the way things were back then.

I'd be interested in hearing how it all works out. Back in the nineties, Eritrea seemed full of passion and excitement, with a sense that everything was flowering after the long, brutal civil war. It hasn't gone very well since, but maybe this time the flowering will continue.

Hope that's helpful.

Mark