Hi,
the default calc search refuse to be advanced which is annoying, it do not set search “all” sheets by default
I run LibreOffice Calc - version 3.5 (on Windows 7 - home edition 64 bit).
To get this feature you should:
- Press Ctr+H (shortcut) in order to get the “Find and replace” window;
- Click below on “more options”;
- Click on “search on all sheets”.
From this moment on, you are able to search your data on ALL sheets
I have tried to close Calc 3.5 and to reopen it.
The option to search on all sheets is still activated (no need to click on it one more time) 
To recap, this feature is available in Calc 3.5 as well (not only in Gnumeric).