Just finished a mission I set myself to clean out the UK Tagwatch (http://tagwatch.stoecker.eu) a bit. Don't panic though, I haven't been bulldozing away all the new and novel tags people are using, just going through it all carefully with a duster and having a go at the following:
*Fixing spelling mistakes. By the nature of Tagwatch, this mainly means spelling mistakes in the tags, not the values. For example, I'll definitely have caught amneity=parking, but not necessarily amenity=praking. Also I might have left a tag or two that was obviously only being used by one person as *all* instances were misspelled. ;-) This category included trailing spaces, although I think a lot of these get auto-fixed eventually even if I don't bother...
*Nonstandard -> standard tags. This was by far the biggest job, as these are trickier to spot by users outside of Tagwatch. Let's face it, we don't all remember the entire Map Features page all the time, and so sometimes we put max_speed instead of maxspeed, or think the tag for phone numbers is "telephone=" instead of "phone=". I know I do, since I've embarrassed myself by turning up plenty of my own mistakes like these as I've gone through...! Unfortunately some of the most common mistakes were made just too often to be fixed by hand by me in any sensible time: if anyone feels like finishing off "telephone=*" then go ahead, but you're in for a long job!