i'll throw my hat in here, i've got several and most are all in use for some purpose
two t7500 - one is a dual x5675 xeon with 36gb of ram, running quadro 4000 gpu still and windows 10. right now its my plex server and does some light in home streaming until i get another workstation up.
the other t7500 has a single x5675 and 24gb of ram along with 4 1tb wd hard drives. running freenas 11.1 and serves are my nas and ubiquity controller for my AP
t5810 - lower end quad core xeon 2.8ghz (can't remember the model will fill in later) and 32gb of ram and a k2200 4gb gpu, 512gb ssd from samsung. its going to be my main workstation with cpu upgrade sometime when the prices come down for 2011v3.
t3610 - also a quad xeon ~3.1ghz with a k420 quadro and will be my wifes main workstation
t3500 with one xeon x5675 and 12gb of ram and quadro 2000 gpu, was a test box just to play around with cpu mining a few months back...its going to be repurposed as my projector pc upstairs.
older precision 390 that i was trying to get a sticker modded e5420 xeon to work in it. currently a core2duo of 2.4ghz or so running with 8 gb of ram. hoping to just have it setup with linux mint or as a fun box to play around with, not sure yet.
i've got a few older optiplex's around too but they aren't exciting, i get some good hand me downs though and really like the build quality of the dells.