Not that useful, but should be possible.
This method frees up a lot of RAM space, since rooted phones won't probably need /cache.
See this Howto about activating JIT on the Milestone's Dalvik VM. It speeds up certain operations.
Native support for Free Lossless Audio Codec.
Here's a module for supporting FM radio on the Milestone/Droid. Includes example application.
And here's software extracted from the XT702 which allows to use the FM radio there. It could be made to work with the Milestone, perhaps.
NOTICE: Unfortunately dproldan has concluded, after disassembling his phone, that the Milestone lacks critical traces and components to support the FM radio capabilities (both tx and rx). So FM radio tuning and/or transmission seems to be completely impossible on the Milestone. BTW, he also ruled out TV output for the same reasons.
This project allows to overclock rooted Milestones. Usage instructions are available on that site's wiki. It requires the use of SetCPU to make the change persistent (see also here for more information about SetCPU), which would need to be called from the phone's modified initialization script (see below). User qvr has made a patch in order to make SetCPU not necessary (included in the milestone-overclock project kernel module since version 1.1). There's another patch that fixes the CPUfreq statistic by setting the frequency changes also in the stats frequency table. This patch also fixes the handling of writes to /proc/overclock/omap2_clk_init_cpufreq_table_addr (Issue 30). You can try it here.
Note: the vsel value used with SetCPU should not exceed 96 decimal (0x60 hexadecimal) according to this formula. But see Note 2, because any change in vsel risks destroying your CPU.
Note 2: user katsuru has had his Milestone die after overclocking it stable for a day at 1000 MHz while undervolting it to 62 mV. The phone became really hot (“though not as hot as when playing Homerun3D”) and then failed to start at all. Some people think it smells like it is burnt. His CPU might have been not very good because his phone would reboot within 2 seconds of setting it to 1200 MHz at 80 mV, but we never know how good is our CPU until it's too late. So beware. Update: user cobani had his Milestone working “fine” (supposedly) at 1000 MHz @ 62 mV, but within seconds of changing it to 1200 MHz (keeping voltage at 62 mV) his phone was fried.
It is also possible to replace the default (“ondemand”) governor with:
These hacks are independent from the overclocking, but since it's power-related it's been placed here.
This post details how to replace the default Launcher application with the ADW Launcher (which otherwise would not work on the Milestone).