Roll-up 3 for AX2009 RTM and SP1 is currently under development and planned to be released to PartnerSource and CustomerSource in mid-September.

The roll-up package will contain both a cumulative kernel update and a cumulative application update. Although there is no dependency between these two updates, MS recommends both of the updates are installed together.

The roll-up will be installed on P-layers (i.e. SYP and GLP) and update the SYS layer as well as the GLS layer that is installed on the system. The roll-up is going to carry several country specific functionality.

Depends on various aspects. For instance hotfix roll up provides code fixes on various areas.  If you have made any modifications in those area it might create compilation errors, loss of functionality etc.   In such cases, you might want to involve your partner.