We were aware that some miners did mine OP_RETURN.
We do have plans to move this. We previously decided against because we felt it might take too long for the transaction to get confirmed and wanted to at least wait til there is at least 50% pool market share that mines OP_RETURN.
On second thought, we might move to OP_RETURN in the next week, I will certain evaluate this a bit more tonight.
The backup plan is still to move to OP_RETURN once v0.9 is adopted or more miners start accepting OP_RETURN
Please move to OP_RETURN ASAP. Right now, you're making money off the storage of 1000s of people like me running bitcoind, with no ability to remove your messages.
If people are really wanting something to be stored forever, is an extra hour or two really going to matter? BTCGuild is accepting OP_RETURN, along with several small outfits like Eligius, so it won't take days on end to confirm.
EDIT: As does eligus (they have always accepted nonstandard transactions).