I would say it was decent or acceptable but nowhere near blazing fast. I had a rar of misc business documents that was over 1GB that I archived not long ago and used that as my test. It took a few minutes to unpack it, I expect that it was not any slower than copying the rar, extracting on my workstation, and copying back and probably faster than using unrar over the network.
I just posted unrar for the droboshare this afternoon but i have no way to test/verify it since I don’t have a droboshare. If anyone who is interested tries it, please post here if there are any issues. Once I get confirmation, I’ll remove the BETA label from the download link for it.