BLPE was reasonably good, but the developers were clear it would never run in Classic mode inside OS X. It also outlived most of its competitors, which should be a sign.
As a longtime BLPE user, I've been part of the beta program for GuestPC; they never told me it was safe to come out and talk about it (it came with an NDA only slightly less restrictive than the PATRIOT Act). Win95 and Knoppix 3.7 booted/installed just fine (as did the SLAX microCD). The trouble I had was with networking in W95, and I forget what dead-chicken waving seems to have fixed it. The trouble I had was installing W95: the opening screen requests your Windows serial number and it uses the 98 and later serial validation scheme. I think I ended up padding zeroes and it worked.
Most Linux liveCD distros run fine --probably because Linux does a more intense job of detecting hardware and dealing with it-- but like most emulators for most platforms, you do best with .iso images rather than regular CDs. Since Apple Disk Utility makes ISOs with no difficulty (regardless of the filesystem on the CD) there's no reason not to do this.
I started with Blue Label for OS 9, and they were cool enough to keep the updates free (I paid $25 for it back in 2001). In those days it could be set to run as a bootloader and ONLY ran in fullscreen mode.
GuestPC is not a mountain of suck like some people have said here, but I haven't tried XP on it yet. And you'd have to be an idiot to try gaming in an emulator regardless of host/guest platform. Mainly what I find it useful for is certain Poser file manipulation utilities which are only available for Windows. Then again, I work in an academic environment where I can buy a used Optiplex GX1 for $200 and XP Pro for $10, so my burning need to run Windows on a Mac is diminished somewhat.
This is coming from someone used to running Jaguar from PearPC on a Dell and Linux inside Bochs, so I'm used to emulator config hassles. Networking is the hardest part, usually. What I miss from Blue Label was the ability to do more configuration options; the version I have still has "Preferences" greyed out.
What you get for your money is the knowledge Microsoft isn't pulling strings somewhere to disable something useful. It may not be open source but trust me, it isn't a ripoff or something else rebranded.
