In RP 3.32 it seems that the 'Previous product' and 'Next product' text links on showproduct.php are erratic... sometimes they display and sometimetimes they don't. When they do display and your click on 'Next product' and move on to the next product, there may be a 'Next product' link on that (second) product but more often than not there is no 'Next product' link.
It's not just happening on my site... I've had a look at
http://www.reeftalk.com/reviews/ (Chuck S' site) and it's hapeening there as well.