Yes lots of experience with it.
All the ATi cards since the HD2900 can do it internally, but they need special adapters (comes with the cards).
Many of the nVidia cards since the Geforce 9600 can do it, but most add the audio externally via SPDIF input (cable pair, co-axial, toslink) on the card which then gets combined with the video signal. The adapter restrictions are a little lower and more often than not a generic DVI->HDMI adapter can be used.
Do a search of DVI to HDMI audio on google and you should get more than enough info.