I use a system that's similar to many that have been described, but use slightly different words to remind me of my intent:
1 - Other (test photos, WhiBal shots, etc.)
2 - Record ('This is how the house looked when they tore the siding off')
3 - Snapshot (most family activity pictures)
4 - Print (These I'd be willing to hang on the wall)
5 - Portfolio (These are the ones I'm particularly proud of)
As to leaving the top rating until I'm a better photographer, I don't find that necessary. Not because I'm that good now, or don't expect to get better, but because I have very, very few images now that fit my current criteria. As I improve, I hope that the proportion will increase. And, if I suddenly find myself drowning in 5* images (fat chance), I can always change their ratings.
On import, I assign all images a 3* rating w/ my import preset. As I make my first pass through the images, I cull out the deletes w/ the reject flag and assign 1* and 2* to appropriate images. None of those receive further processing. The rest get initial processing appropriate for family photos. Then, I run a slide show of the 3* images to pick those for further processing and 'possible' upgrade to higher ratings. In other words, I don't initially assign 4* and 5* ratings; they have to be earned by living with and working with the images. And, after working w/ an image, I often down-rate it when I decide it just isn't as good as I initially thought. Just another, slightly different take on the subject that happens to work well for me. Cheers,