The problem with metrics is related to the problem of work estimation. The remark I usually make is something like

If I've done it before, then my estimate of time will be nearly 100 percent accurate. If I've never done anything remotely like it then my time estimate will be a wild-eyed guess. If between these two extremes, scale the reliability of my estimate accordingly.

Roughly translated to your situation, a 'good' number of lines coded must also be based on a sliding scale, typically related to the amount of experience you have on similar projects. More to the point on some projects, 50 lines might be a near super-human performance, so there is no hard and fast rule here. The good news is that lines of code as a metric is at least bounded, zero on one end and some largish number on the other (human limits and all that)!

--hsm

"Never try to teach a pig to sing...it wastes your time and it annoys the pig."