Do you want a bleeding edge product or one that's more tested and stable?
How unstable is the DIR-655? I really don't know. But some products like these were rushed out too quickly, and have growing pains. And of course 802.11n is very much a work in progress.
I'd be tempted towards the DIR-655, but only if I was prepared to take some risks. In light of the work-in-progress, potential uselessness of current draft 802.11n, interference issues with 802.11g, additional cost for wireless adapters, not so great wireless performance in some cases, etc., I'm not sure that the risk is justified.
Still kind of a tough call though -- the DIR-655 could end up morphing into a standards-compliant full replacement for the DGL-4300.