Don't sweat the details. Don't try to exactly convert everything one-for-one. There's really no point.
Figure out how fast progression should be. One of the reasonably nice things about the adventure paths is they're designed for a steady and even level progression, and 4e excels at that. In each section see what the expected level entry points and exit points are for the section, and then figure out generally how many encounters you're going to need.
or
Don't even bother with equating XP to levelling: focus on the interesting encounters, build those, and use the narrative flow to level the PCs instead. (That is, the adventure path says that "at the end of this section the players should be about Lvl 4"... use those comments to map out how the PCs should level as they go through the adventure, and forget about XPs.)
Find the cool magic items. Be careful to notice where the magic items get handed out in the 3.x AP, and then figure out where those items should go (which PC), and which items you should hand out in 4e terms. Notice that items in 4e are much more stratified and tied to the general experience level going on in the adventure than in previous editions. I have found in my own experience that magic item planning is the hardest part of the conversion. Luckily, the 4e path to building encounters give you decent guidelines on how much treasure and items you should be kicking out to the players.
Don't forget about rituals. Rituals are much more central to 4e than previous editions, and you should consider them a cross between cool encounters and magic items; when/how will you kick out rituals to PCs, and require that they use them to solve a problem. See if you can identify points in the 3.x adventure path where a ritual might be needed or used to good effect.
Forget skill challenges. Your mileage my vary but we never really thought that skill challenges worked, especially if you're levelling your PCs narratively rather than by XP counting. Instead, when a situation arises that is a complex problem to solve (convince the local baron to lend you guards for your raid on the bandit cave) focus on going around the table, asking people how they're going to contribute. If few PC fail with their contributions than succeed, that's an indication they've succeeded, but pay more attention to what they say about how they're contributing than what their rolls are. Lean heavily on "helping out" rules: success against DC10 adds +2 to the lead character's roll.
I ran portions of Rise of the Runelords and Second Darkenss with 4e, with two different groups, followed these general guidelines, and things worked out for me.
