I'm in a slight quandary about this as well. I did my IMC last year and have had it since November but have not yet had any real IMC conditions without an instructor in the right hand seat. Given the sort of weather we get here the intention in having it is to allow me to fly more days of the year and stop cancelling trips but I am not too keen in getting into habitual 'hard IMC' flying.
What I have done without an instructor on board is to fly 90 miles across country and back on a day where there were no clouds but the vis. was only 3km. This was an eye opener - once I got up to 5000 feet I may as well have been in the clouds since I could barely see the ground below me, had no horizon worth talking about (in fact I had a sort of false horizon which had I levelled the wings against would have had me going round in circles in a 20 degree bank!). I also took off into a 1500 foot BKN cloudbase one day in the knowledge that I was chasing the clearer weather which had been upon me an hour earlier. I climbed through holes in the cloud and popped out on top at 5000 feet and sat there quite happily until the clouds receded and I was in perfectly good VMC again. Neither of the above would have been legal without the IMC but were not that hard.
With an instructor on board I have flown a short IMC flight of 15 minutes each way (to Bembridge) where we popped up into the cloud and sat in it each way for most of the trip across. On the way back to Goodwood a layer at 800 feet had descended over the airfield so we descended below over the sea and then flew back to do a bad weather circuit to land - this one I would not be happy about doing on my own!! I have also been up for a few local flights to pop above the cloud and do some VOR tracking in the sunshine and have flown across to Farnborough to do their ILS (which was free at the time as long as you didn't land) which was in cloud from about 1500 feet AMSL (so 1350 feet AGL at F'Boro). These have been hugely useful experiences.
I read the GASCO article. I got to the end of it feeling ready to go and try some of the suggestions and then read the editors note where it says that "some instructors advise against seeking out cloud in which to practice instrument flying" which confused me totally! The article is saying you should get up there on your own and start building up your confidence. Then the editor comes along and says moreorless "you can try this but some instructors would advise against it! Great!!
Anyway, I plan to continue to push my boundaries little by little. I have also dug out my copy of FS2002 and am using that to simulate instrument approaches into airports I already know. This gives me some way of visualising where in the world I am rather than just knowing where the airport is - I use Southampton a lot. I find it quite useful if I can imagine where I am on the chart! I set up the simulator to have a cloudbase of 700 feet and tops above 10000 so I go into cloud a short time after take off and can't see any ground until quite late in the approach. This is really helpful.
I now intend to follow some of the advice in the GASCO article - but I have this strange hankering to invest in an electric backup AI before going too much further!