I'm involved in the European Stardust network [3] and am working on remediation technologies for space debris. There are some particular candidates for active removal that we know pose a great risk. One of the highest-risk objects is Envisat [4]. There's a concerted effort in Europe through the Clean Space Initiative and the e.Deorbit mission in particular to figure out how to remove large, dead satellites like Envisat [5].
For the last six months, I've been working on building a model for preliminary design of missions that could potentially target multiple debris objects in one shot [6][7]. Turns out that it might be more cost-effective to design multi-target debris missions (paper will be o arXiV by the end of the year).
As of next month, I'm going to be leading a new project called Scarab that'll last 12 months. I'm going to be working with a team to develop an end-to-end simulator for the removal of dead rocket bodies (e.g., Ariane) that pose a significant risk to operational satellites, focussing on robust Guidance, Navigation & Control for proximity operations.
So yea, there's a lot of work being done in the field and there's a general consensus that we need to act now to subvert the doom scenario of an uncontrollable collisional cascade that will most definitely render vital orbital bands useless.
[1] http://onlinelibrary.wiley.com/doi/10.1029/JA083iA06p02637/a... (paywall)
[2] http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/2014000...
[3] http://www.stardust2013.eu
[4] https://earth.esa.int/web/guest/missions/esa-operational-eo-...
[5] http://www.esa.int/Our_Activities/Space_Engineering/Clean_Sp...