I didn't have a problem with my (60GB) or my son's (20GB) 360 after the update. Not using HDMI however, so it might not have affected me anyway.
I do have a 3rd core system which took a dive on me a few weeks ago, stopped reading game discs, although it reads everything else just fine. Oh well, called MS on Friday, they sent out the UPS Box, which I recieved yesterday and sent it out this morning. I asked for the DVD-rom and motherboard to be replaced with the Opus or Jasper version, since the one I sent in was a launch Xenon version.
Will know if they actually do it, since they'll need to include a new power supply with it.

The last 360 I sent in for repair (the one my son is currently using now) was only out of commision a total of 5 days. I called on a Monday, had box on Tuesday, sent out on Wednesday and recieved it back on Friday.
MS has been very good about the repairs (IMO) from my own experiences and from what my friends who've also had problems have told me. It's disappointing that there are problems to begin with, but my 2 launch consoles have always been repaired within a matter of days if they took a nose-dive. Happy to report that my 60GB version hasn't had a single hiccup and is so much quieter than the launch versions (thank you die-shrink).
My PS3 (well my son's now) has never had a problem.. well except for the fact it just sits around collecting dust with the occasional Little Big Planet diversion.