Eight Sony engineers at NAB said it couldn't be done, but we found a way to retrieve deleted clips off an SDHC card in an MxR reader from my EX1.
Obviously it occurred by my own "operator error" that the EX1 workflow makes too easy to do. Doug Jensen comments on this in latest EX Manual (Page 24, Tip#10)...Never have more than one card at a time in the camera slots (with a few exceptions of course). That's how it happened. Just finished shooting on card in slot A... put another card into slot B to delete clips. Switched to Media mode to make sure those were the clips I wanted to delete. When switching back to Camera mode, it must go through the Off position and then on to Camera mode. That part has the camera default to the A slot...which I did not notice. So I go into the menu and merrily begin deleting All Clips... and then look up at the viewfinder to see the A slot is selected...and I melt into my socks.
Carefully, after letting the process complete, I extract the card and not let the client see my blank expression. My hope is, the data is still there since I have not over-written the card and that the card's Table of Contents simply has a code change that says it's OK to record on.
Searching all the Forums, it seems no one has ever had any luck retrieving deleted data. We have a utility that saw the files but couldn't playback anything. There was hope...maybe. Sent the card to Sony Data in Atlanta...they worked on it for a week... No luck. Their biggest complaint: Sony Japan would not help them out in unlocking the proprietary code. The next week I'm at NAB grilling every Sony rep, VP, and Engineer I could find. Most simply shook their heads saying it probably can't be done because it was an SDHC card and not a Sony SxS card. Then we found a Frenchman living in Barcelona, Spain by the name of Benoît Joossen ( supportcw@mac.com ) who has a company called Aero Quartet. He thought he could do it with his custom software (the man is a genius!). The process is a bit complex where first all the pertinent circumstances and information are sent to Aero. They then send back a "customized" scan program to search the device for the types of files we're looking for. That is sent back to Aero Quartet in Spain and they send a trial retrieval "customized" program. If it appears that it will retrieve all the files we're looking for, then we can send them payment for an unlocking code. It was an absolute bargain at $170 relative to all our bad alternatives. These guys walk on water.
I'm still smarting over the fact that Sony doesn't provide this as a service to their camera customers. I would have gladly paid them... if it weren't for that bit of arrogance from Japan. Maybe they'll add an Undelete function to the next Firmware update... but I'm not holding by breath with the current attitude from Japan.

Most simply shook their heads saying it probably can't be done because it was an SDHC card and not a Sony SxS card.

Shameful attitude and lack of knowledge from Sony there. Regardless of if the media is SxS or SDHC, the media is formatted exactly the same way (i.e FAT32). If you have a deleted clip it would make no difference what the media is as it's the file system used on the media that is important.

Glad you managed to recover your clip. However it does highlight that you should never be formatting media or deleting clips on location. Take enough spare media with you and do the formatting back at the office once your media has been safely transferred.

Yes Marcus...That was a hard lesson learned (which is why I posted it for others here). And as Doug Jensen points out, never have more than one card in the camera at a time...Especially if you're going to do some process on that card.
Now, some of the Sony engineers claim that there is a difference in how data is written to an SxS card as opposed to an SDHC card. What I think they're referring to is the "wrapper" around the MP4 data which is Sony propriety code on the SxS card. That's why that said they might be able to help if it been recorded on an SxS. Some started to claim Sony doesn't support recording to SDHC, which is why it will be next to impossible to get the data off the SDHC card. I had to point out that right over their shoulder was a display with the new Sony brand SDHC cards, right next to the new Sony brand Flash 34 adapter for SDHC cards, right next to the new Sony NX5 camera that has an HDSC slot... What do you mean Sony doesn't support that??
Turns out, as you were saying, Aero Quartet went after the MP4 files around the Sony proprietary code. You would think Sony would offer that as a money-generating service to their customers...but there is a certain engineering arrogance out of Sony Japan. And the US Sony guys did feel terrible about the situation and tried to help the best they could...even offering to buy me a beer!