Same useful tips is that in case you have Microsoft software contract like Volume licensing etc it might be that if you download your CRM software it is still RTM version. It will help to just download version from the internet which usually already has latest roll-up applied.
Ok, some of you are a bit scared to apply the latest roll up you could download a previous one too.
Nevertheless common issue as my roll-ups cannot be installed might be due you already installed CRM which includes the roll-up you try to apply. Also reading the notes with roll-up can be handy so you now you first have to apply roll-up 6 and then 7 or 8, depending how much cuts you have ;)
Same easy site that gives you overview of the rollup can be found:
CRM 4.0 ( might be time to think about upgrading )
CRM 3.0 ( really time to move ahead)
In case you want to have any idea when the next one will be available go here. Please notice it is "Projected" which basically means if you lucky we have it and else you just wait a 'bit' longer...
Time to keep track of your build number!