Would robert's concerns about Minefield/Firefox also apply to Seamonkey?
quite possibly. i use minefield regularly, i'm even using it in 2.x and it's fine. note that i'm not making a backup i'm using cloud (but when i use usb and run backup, i'm also using minefield.)
the big difference is i clear my cache when i'm done, and i don't use the massive bookmarking features or keep history set for 90 days (that is a stupid setting, blame mozilla.). you can also set your cache to something more reasonable, but clearing private data when you're done makes all the difference in the world. if i ran backup right now, minefield would not be an issue.
you can also just add the cache (and anything else you don't want to save from boot to boot) to .xfiletool.lst ... i really don't understand why the bad review of minefield. configured properly it shouldn't be any different than any other browser. but if you use it "out of the box," robert's right, don't back all that up you won't like it.
one other thing is flash. without flash many sites are faster. on an old machine using flash9 instead of 10 helps. using 1.x instead of 2 might also help, but 2.0 isn't even release yet, we'll see.