I've had mostly positive experiences regarding talking to and making friends on Last.FM. I usually talk to people with similar taste and the conversations starts off with: "Hey isn't insertbandhere great? What's your favourite song?" and things go from there. The topic veers off of music into other aspects of life after awhile. I think the longevity of the conversation depends on the person and if they have a lot to say. If it's the usual: "Oh yeah, that's cool." I just give a thumbs up, not much you can do with that. :P

I try to reply within a day or two, but there's times when I'm stupidly busy for a week straight and can't get a reply going. Most users either take awhile to reply or they continue the conversation like there wasn't a time gap. Most people are understandable about reply times.

I've met some really great people on this site. Some I've been talking to for 4-5 years now, either through last.fm PMs or we've moved to FB or Skype. I take conversations as a give and take - I ask about the other person and while they give info they also ask questions in return. If it's short or one sided they don't tend to last long.

I'm a very talky person and don't mind multiple conversations. It can be a hit or miss with active/inactive users, but there's still some of us who like chit chatting. :)