osx has the really powerful dtrace/ktrace/dtruss tools - however i'm not willing to invest the time necessary to learn dealing with them right now.
what's the easiest way to get the equivalent functionality of linux ltrace (and possibly strace) on OSX?
No answer for ltrace (except perhaps "work out how to use dtrace" :-) ), but for system call tracing ala strace, dtruss is a pretty good front end to dtrace.
e.g.
dtruss df -h # run and examine the "df -h" command
dtruss -p 1871 # examine PID 1871
dtruss -n tar # examine all processes called "tar"
I'd suggest that DTrace is not as complex as you think it is. I just wrote a two-part tutorial on using DTrace to tune Cocoa applications for the Mac or iPhone, which can be found here and here. I came into it thinking that DTrace would be extremely difficult to work with, but it turns out to be reasonably straightforward to use.
you don't need to learn dtrace to use it. there are quite a few dtrace scripts that come with OSX. To see an (incomplete) list:
man -k dtrace
In your case dapptrace might do the job.