Like conaill said- it sounds like you're mostly doing intrigue/ mystery stuff for the group. A lot of groups don't like this sort of thing; it's sometimes hard for people to wrap their head around it. There's also a fine line between what is obvious to the DM and what is completely lost on the players. A lot of players get stuck, the DM won't help them out, so they just decide to not bother with it and head out to loot some monsters instead. This sort of thing depends on a lot of variables- your characters, your players, the plot, how you're your running things or distributing the information, etc. Really, too much to go into on the boards.
The key point here is- there's no reason why a heavy roleplaying session should be all negotiation, maneuvering with NPCs, digging up secrets or the like (I blame all of this on White Wolf, as they've convinced people that roleplay has to equate to dirty political intrigue. But that's for another thread...)
My suggestion- take a session or two off to do some light-hearted campy type stuff. Send the players into a new town, have one of them mistaken for a local villain, someone else gets conned into stealing something from the mayor's house, that sort of thing. Just let them hang out, meet people at the tavern, get drunk or loose all their money gambling. That sort of thing. They could take to this type of NPC interaction much better than they do the cloak & dagger stuff, especially if they're new players and not used to how RPGs work.
Basically, treat it like a site-based adventure only without the monsters- they're exploring a town, and interacting with odd (or even normal) NPCs instead of monsters. The interaction is likely to be different, since the NPCs aren't threats and (presumably) don't have much that the characters want. The NPCs can then lead the way to small encounters with minor monsters, such as rats infesting a local temple, a band of orcs that keep raiding the same pie shop, that sort of thing. Then, in addition to rewards from the quick encounters with monsters, the PCs also get gratitude and help from the NPCs, giving them more reason to pay attention to people around them in the future.
If you're totally stuck, I recently picked up "The Goblin Fair" adventure from Airweaver Games. It's their only module to date, but its totally awesome. There's a few minor fights to keep the PCs from getting bored, but most of the module is just interacting with quirky (nigh-on insane, really) NPCs and trying to find some sort of magical key. The module's also structured so that you can get them the info to get to the end pretty much whenever you like.