creativepro -
I think you should definitely upgrade to 1.2; it's a big step forward.
Your existing Presets will not be affected by the upgrade.
You can manually add/remove/change presets; under the Help menu select "Go to Lightroom Presets Folder". You'll see all the different types of Presets in their own folders.
Re: cropping preset to specific aspect ratio - you can save your own Develop Preset for this; it's easy to do. Just crop an image the way you like (and save the Crop ration in the crop ratio list); then click the + symbol in the Develop Presets Panel to make your new preset. Give it a descriptive name like "6x4 Crop". (Note, however, that 6x4 is the same as 2x3, which is already in the list). You can use horizontal/vertical versions of the crops.
Re: concern with upgrading - as with any software, different people will have different problems. It all depends on your computer and OS. I'm not sure what issues you are referring to... I'm using Mac OS X Tiger (10.4) and have moved all the way from Beta 2-3-4, to 1.0, 1.1 and 1.2 without a single hitch.
Good luck!