GeoHot has just released a new Limera1n exploit for iPhone/iPod Touch devices running 4.1. It currently does note support the 3GS with the latest boot rom, but the website indicates this is being worked on.
Instructions are included with the app, but detailed instructions are available at Redmond Pie.
It is still in beta, so there are additional updates/tweaks to come.
I was unable to get my iPad running iOS 4.2.2 beta to work, but I will try it on another PC later.
I am currently downloading the 4.1 update for my iPhone 4; it is a 589MB firmware, so it is taking a few minutes to download.
If this does not work, the SHAtter exploit is due to be released tomorrow…