In router or modem mode ? I have had a horizontal SH2 for years with no problem it is fairly "open" though. If it were in router mode I would expect it to alter you wifi environment as you are turning the internal antennae through 90 degrees. Whether it will make it better or worse will depend on a number of geographic factors on which others should comment. I would just do it and see what effect it has.
-------------------- John --------------------
My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired 2 WiFi,) SH2 in modem mode with Airport Extreme Router. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.
Interesting question. WiFi traditionally uses Vertical Polarisation. The aerials in a laptop's screen surround are more or less vertical, the internal aerials in a hub or router are also near enough vertical.
Laying your hub on its side will result in Horizontal Polarisation which in theory will mean weaker signals between it and your devices.