Ale,
There is no restriction on the number of uplinks connected to a 3560 switch and is mainly dependent on the number of ports available.
in case you use fiber, then the uplinks are limited to 4 as there are only 4 SFP ports available
The one you are referring to is mostly the etherchannel between the swithces. In this case it is true that it is limited to 8 links.
HTH
Narayan