I don't really do HTPC, but at times I want to connect my PC to the HDMI port of my tv. I discovered i needed a Displayport to HDMI converter to do so, cheap enough.
Are those adapters all created equally?
Will it be able to pass the full HDMI resolution across with the whole conversion from Displayport to HDMi going on without losing anything in between?
I believe so. AIUI Displayport can work in a number of modes. When it runs natively it uses its own standards for video, but when connected to a DVI or HDMI cable, it effectively switches into an entirely DVI/HDMI compatible mode - effectively becoming HDMI or DVI. The cables are very low-cost, so aren't actually doing any video processing or conversion.
There are situations where Displayport can carry content that HDMI displays may not be able to accept (Panasonic are using Displayport as a stopgap on their 4K displays before HDMI 2.0 is available to allow 4k/60p connections - circumventing the HDMI 1.4 limit of 4k/30p) However in the situation where you are feeding a regular HDTV - you should be fine.
I used to connect my Macbook Pro to an HDMI display using a MiniDisplayport to HDMI converter. No problems at all. No quality loss.