People complain about this a lot, but the rate of link-rot of ordinary URLs is much, much greater than people believe. I run a URL shortener, and I can assure you that while all of our links still work, huge numbers of the pages they point to no longer exist.
The problem is also overstated because nearly all URL shorteners (bit.ly included) are sending HTTP 301 responses. This means that the short link is never indexed; only the original link is. So shorteners have no effect on pagerank/search results, which is where the longevity of pages is important (since anything not published in the very recent past is mostly discovered by search).
The problem is also overstated because nearly all URL shorteners (bit.ly included) are sending HTTP 301 responses. This means that the short link is never indexed; only the original link is. So shorteners have no effect on pagerank/search results, which is where the longevity of pages is important (since anything not published in the very recent past is mostly discovered by search).