So its time to upgrade the slugs Debian NSLU2 from Etch to Lenny. Every upgrade carried a risk, depending on how much you have customised the installation. In my case, the risk was small since I have made little change to the default install.
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In spite of that, the hassle and significant time penalty in making a fresh install was a main factor of consideration. A little extra effort to ensure a fall back path in case of failed upgrade went a long way.