My understanding is that there currently is not one, although rumours abound that one is coming up soon. The best place for "official" information is the iPhone Dev-Team. More direct/recent updates can be found by following various team members on Twitter. MuscleNerd is a good example. If other legitimate groups released anything solid, you will hear about it through them anyway (as is the case here: Chronic Dev Team seem reliable too). There are already fake sites springing up in anticipation of the next release; the important thing is not to use anything that hasn't been confirmed by them or that you have to pay for.
Additionally, if you have saved your SHSH blobs using Cydia on an already-jailbroken phone or The Firmware Umbrella, you can downgrade and jailbreak the old version. Normally this means you can upgrade using PwnageTool without losing your jailbreak, although I don't think the Dev-Team has released something compatible with 4.1 yet.
UPDATE
There is now a full jailbreak for 4.1 and later on 3GS. BigBoss maintains a jailbreak table which may be useful for updates at-a-glance. My understanding is that all current devices are now able to be jailbroken forever (greenpois0n/limera1n exploit), but iPhone 4 and later model 3GS are sometimes tethered on iOS new releases (as of this edit: not tethered on 4.1, but currently - hopefully not for long - tethered on 4.2)
Well since you are using Mac OSX, when you plug in your phone you can do the following to back up your pictures OUTSIDE of iTunes.
Step 1
Open up Preview with your phone plugged in. Go to File > Import Image. You will see it populate all your photos/videos. Save them in a separate folder (maybe somewhere on your desktop), then delete them all from your phone.
If you are concerned about mass deleting these files, you can just do it with SSH. This is after you've imported all your images through preview.
From Terminal on your desktop type
ssh root@your-iphones-ip-address-here
Will prompt you with a PW, chances are if you haven't changed it it's alpine or Alpine. Change directories via the following command:
cd /var/mobile/Media/DCIM
Depending on the amount of images/videos you have you will see 100APPLE/ and maybe 101APPLE/. In the directory type this to remove ALL images and movies in one command
rm -r 100APPLE/
rm -r 101APPLE/
Backup in iTunes now and you have a fresh backup with just numbers/apps/whatever else. You can then import the pictures/videos back if you want after you restore it.
Best Answer
Yes, but a backup of a jailbroken device will restore all jailbreak data such as preference files and other data which will take up storage space on the device.