Are there any long term effects of using dermal fillers?

The only long-term effect of fillers (& I'm speaking about hyaluronic-acid based fillers which are the overwhelming majority of fillers used) that has been shown has been positive, namely that people who continue to have these treatments tend to look more youthful and the filler seems to last longer over time. There does not appear to be any problems such as "stretching out the skin" or creating new wrinkles. 

The Ha families of fillers ( Restylane Juvederm, Voluma, Belotero), Radiesse and Sculptra are not permanent. Although some say that Artefill/Bellafill are permanent I do not think that these companies are claiming that any longer either. I do not use Atrefill and Bellafilll so am not an expert on them but as far as all of the other fillers go I do not think that there are any known long term problems. I have personally used most  of them since their beginning and I do not fear any permanent effects other then hope for some new collagen production from some.