Sure it can be done but whether I would recommend someone new to IFR to generate a load of user waypoints in his flight planning program, and then litter his GPS memory with them, that's a different story.
If one has a GPS which the flight planning program will download to (something to check out before buying either of these items) then the user waypoints should transfer fine into the GPS, but if you make a habit of creating them, you will end up with so many that mistakes are possible.
We all speak with our own experiences and since 2001 I have had to create user waypoints for
1) La Axarquia (LEAX) in Spain, in 2003. By 2004 it was in the Jepp database.
2) Messalonghi private airfield in Greece (near the MESSI intersection), in 2010.
3) A DIY GPS approach into a certain UK airfield. I developed a very nice IAP, with a missed approach, for that place (lots of hills nearby) which uses several GPS waypoints, all on the same inbound track (as is the IAF; there is a procedure turn if you come in from the other direction) and all those up to and including the FAF (the TOD) are double-checked against a nearby VOR/DME. I flew it a few times in VMC but never had a reason to go there in bad wx again...
I wouldn't consider these a good reason for using user waypoints for hacking around the SE of England
