Well, personally, this is how I generally base my buying decisions:
1. Do I NEED a computer now?
If you need a computer now (for work related purposes, or school related purposes, etc), I would get one now. Yeah, in the future, cool new stuff will be out, but if you need it now, the bottom line is that you need it now.
2. How trustworthy is said "event" on the 23rd or 24th or [insert date here]?
There are lots of rumors flying around about what's happening when and where and how much. Is it worth waiting for x days for a supposed update that may never materialize?
When I was trying to figure out about buying my iMac, the earliest I would have been able to get one was March 1st. Because the rumor was that the new iMacs were going to be released on the 3rd, I figured I could wait two days (and if no iMacs materialized on the 3rd, I would just get them as they were). But the 24th is about 2 weeks from now. That's much longer than 2 days. What if nothing happens on the 23rd/24th? Will you be kicking yourself for all that anticipation? Will you be willing to wait longer?
3. There will always be better newer shinier things out there.
Sad but true.

If you can get a computer that meets your needs and will do so for the foreseeable future, then great. It may not be the latest model/version, but as long as it is still performing sufficiently for your purposes, then that's what matters the most for me.
I just got a new iMac, and regardless of Snow Leopard (which I personally don't think is coming out until June/July at the earliest), it's fantastic.
Good luck!