Ya, that's the only reason I hate it. Makes it hard to cut/randomize on them. I mean I don't think you can just riffle shuffle but I've also had those people try to cheat the most. Do really bullshit shuffling techniques because they know there's no good way to shuffle unless you do something they can bitch about like riffle shuffling.
Yeah, I always ask my opponents if its OK to rifle their deck unsleaved. Also, with most people running their prerelease foil, it really sticks out in shuffling.
More important than sleaves- BRING A PEN AND PAPER. Your going to get your d20 in the guild pack, but use paper instead because unlike a die that can easily fall over, you can use a more consistent method to keep track of both players total. If there is a disputed life total, the judge is going to lean towards the player using paper than the guy with a die.