I shall have to write a list of these excellent tips so that I don't forget them. What with working out how to link up Jamstix and a racked ReaDrums, and now these tips, Reaper is finally revealing itself to be the beast I always suspected it to be.
My tip? You're asking me? Erm...right-click everything.
1. Right-click the FX button in a track panel and you'll get a list of "My Folders" from your main FX folder, including "Recently Used". It makes it much quicker to find, choose and insert an FX or VSTi.
2. If you have an FX or VSTi already loaded in a track, right-click on the ENV button in the track panel. Select "FX Parameters" and you'll be given a list of your FX/VSTi's parameters. Choose one and an envelope will appear below your track. Another time-saver.
Thank you to Justin, Schwa, Christophe and everyone else for making Reaper such fun to use.