I personally think Izzy hurts the growth and development of the new bandmembers.
Its not fair to the NEW Guitarist to work their ass off and try their hardest to gain acceptance and respect and then have Izzy come onstage and steal absolutely every bit of their thunder.
I've been saying that since Hammerstein night 4...It was a misty eyed bit of wonderful nostalgia, and a symbolic passing of the torch and tip of the hat, but I walked out of there concerned about Izzy's presence obscuring the other guys' hard work. Not in real terms, per se, but more in terms of fan perception.
Like I said above, keeping it casual is cool...Every once in a while, play a few tunes, jam out...great. When you essentially become a touring member of the band, you're only evoking some people's wish for a full-blown re-union. Izzy joining the tour in the manner he did should not be seen as a major issue, yet the problem lies in the fact that some fans (read posts on this board alone) are so enthused for a wishful reunion that they cannot differentiate between what the reality is, which is Izzy simply enjoying getting up there and informally playing some tunes, and the fanciful idea that this is somehow a telling indication that he IS, or WILL soon be, a full-time member, given song-writing credits on CD, etc...