I flew my glider once without wing tape (too damp to get it to stick) and speed control was all over the place because of the noise.
AFAIK because of legislation changes pilots must now have a Bronze to do a DI without supervision, so no more signing off in the log book. However we do teach doing a DI. Each type of glider has it's own gotchas - or at least each type I've done a DI on.