In March 2012, the 2 mm by 12 mm glass HITAG S tag I'd carried in my right hand since 2005 came out, and a new 2x12 mm tag went in. I'd originally picked the HITAG S for its feature set (writable memory blocks, EM4102 emulation, and a 40-bit crypto feature that could protect the tag's memory and the reader session), but seven years on, it was time for a change.
The removal was the educational part. The doctor spent over twenty minutes working forceps around the tag, trying to angle it toward the incision. The implant had wrapped itself in a small but tough cocoon of connective tissue, and since forceps can't grab a glass tag (it would shatter), they were mostly useful for spreading tissue and gently scraping the connective layer off the top. After five-plus years of pushing the implant up under the skin so people could see it, I finally offered to glove up my left hand and work it myself. We had it out within a minute. I was glad I'd chosen a tag with no anti-migration "biobond" coating; removing a coated tag would have taken some serious cutting.
The doctor advised against reusing the old pocket, so the replacement went in adjacent to the original site with a standard injector. Healing was a non-event: the incision sealed itself within a day or two, and the lumpy scar tissue at the old site resolved over a few weeks.
Lessons, recorded at the time for anyone facing the same procedure: mark the implant's exact position with a surgical pen before the first cut, make the incision right where the tag's end pokes up under the skin, and glove up your off hand from the start; nobody knows where the implant sits better than the person who's been living with it. I posted the full write-up to the RFID Toys forum and a photo set of the procedure to Flickr.