I also had some initial struggles with them....but, here are a few more tips.
Take a look at this site... some more specific info
http://networklessons.com/bgp/bgp-regul ... -examples/
for example using bgp-as-path= ^10784_174_[0-9]*$
should match all routes having AS10784_AS174_* in the path. (i.e. one level deep on Cogent network...AS174)
Similarly bgp-as-path= ^10784_174_[0-9]*_[0-9]*$
should match all routes having AS10784,AS174,AS*,AS* in the path (i.e. two level deep on Cogent network...)
Hope this helps you out.
I use these to set a higher bgp local pref, in the inbound bgp filters.
You have to pay attention to the sequence of the command in the filter.