I think it's impossible to keep on top of everything you're reading.... new series always pop up and get in the way :) I have a tendency to skip a volume on some series in an attempt to keep up if I'm late getting into it. I've been meaning to get Sugar Sugar Rune for ages... it looks so good [and Moyoco Anno's so messed up 0_o It has to be good!]

I'd say Tsubasa is worth continuing, but it's a popular enough series it's usually easy to find- I tend to pick it up in chunks once in a blue moon. More cohesive plot does occur, that it takes awhile. Though after vol.6 does tend to be pretty fun stuff.