Yeah, the PTT hack is great. It's an annoying button otherwise. I have it mapped to Voice Command in my case.
Haven't used the tweaker though. I generally prefer to go hacking into the registry myself.
Here's a couple of others:
Hermes SIM/CID unlock <-- Did this one the other day. Worked beautifully.
Hermes Extension ROM Unlocker/Unhider <-- Did this one too. Cleaned out some junk that Cingular puts in there that I don't want installed during a hard reset.
Today Plugin that allows you to change between GSM and WCDMA <-- I use this one as well. I love it because I frequently find myself on fringe areas of 3G.. I like forcing it to stay GPRS.. Easier than putting the band page back into play.. Much faster..