You should be able to preserve settings between 1.5.7 and 1.5.8, but preserving settings from 1.5.6 or before when upgrading to 1.5.8 will still cause major problems.
New in 1.5.8:
- USB Storage Section now supports sharing files via FTP
- USB Storage Section now supports sharing a subdirectory on a drive instead of the whole drive
- USB Storage Section now supports configuration of multiple users
- Fixes 3G Support (broken in 1.5.7)
- Fixes use of non-standard DNS servers (broken in 1.5.7)
- Fixes printer sharing (broken in 1.5.7)
- Fixes bug from blocking of MAC addresses assigned a static IP that connect from a different IP, when appropriate setting is checked
- New Dynamic DNS services: no-ip.pl and dtdns.com (Thanks to Cezary Jackiewicz for this patch)
- Fixes bug preventing NTP daemon from starting properly after time settings are saved (Thanks to Chris Nesbit for this patch)
- Fixes Display of DNS servers in overview section
- Display router hardware model in overview section
- OpenWrt version upgraded to Attitude Adjustment Beta 2 (1.5.7 was based on Beta 1)