"Hey friend, it looks like you are using Opera. Beware, pal, that we don't go to the opera down here on the ranch, so there may be rough-riding ahead! Try one of these nifty browsers buddy, or sally forth into the unknown. OK, pardner?"
You can put all the disclaimers you want before a use and they will "venture forth into the unknown". However, they will ignore (if they even read/understood it) your warning and then bury you in support tickets, complain loudly to their friends, and leave you with a mess to deal with and no real clean/easy way out.
I second this... users rarely read anything & remember even less. If you let them in, then they expect it to work. Its unfortunate for Opera, but we're doing the same for our beta launch.
