Personally, I would wait until the conference because you never know what they will announce...even if they don't have updated PB's (which they won't) they might annonce something that appeals to your liking such as new software which might only be avail. on the new books, other special offers or deals or something else that might appeal to you...so unless you absolutely need it now, wait a few to see.
Don't plan on getting tiger unless you want to wait until at least sept or oct! They are only previewing some Tiger features...this is often very confusing...TO BE CLEAR...YOU WILL NOT own tiger until OCT at the earliest...and unless you wait until sept or oct. buy, you won't own it without paying at least $130+.
Panther is awesome and I personally would wait to get Tiget until December or early next year. There are often bugs to the first release of a new OS (yes, even on Macs 🙄 ) so unless you like to trouble shoot it is usually best to wait a few months at least. The release after Tiger won't be coming out in 2005 anyway so don't think to yourself you will be so behind the curve by waiting...apple has said they are placing more space between major updates after Tiger's release.
good luck.
Johnny