I have been Bulkregister's domain management consultant for almost two years, and helped build out their current domain management system and provided a "domainer wish list" of features for them. They have followed many of my ideas and those of their large portfolio holders, and built out what I consider to be the best domain management system for bulk domains available. I may be biased (I am), but BR's management of large portfolios puts every other registrar's to shame, including Enom's.
I can't comment on the actual sale to Enom, but I can suggest to BR customer's -- if you like what you see on BR, make it known to them. You've probably received the feedback email and login notice - take advantage of it and try to be as detailed as possible in describing to them ALL the features that make you a BR fan.
Let's hope this is a good thing...