FYI, I’m one of those users running on SUN JDK1.5 and thus far I haven’t encountered any specific problems that I could relate to 1.5. Using both Windows XPSP2 and Debian GNU/Linux testing with Eclipse 3.02 and MyEclipse 3.8.4.
I also tried the JRockit 1.5 VM for a while, and no problems there either (although Eclipse felt a bit slower with it, so I changed back to the Sun VM).