Show of hands? I do.
Actually, Windoze cheats and stores the IP address for (my guess) about 12 minutes. The typical cheap wireless router does not store DHCP leases in some kind of non-volatile cache. It would be nice, but it's not economical. Instead, on power up, it re-populates the ARP cache with sniffed MAC addresses, and then uses RARP to re-populate the corresponding IP addresses. With most Windoze clients, you can power off the router, go away for up to 12 minutes, and come back with the same IP addresses. After 12 minutes it's somewhat of a crap shoot. If you've ever had to deal with Windoze XP retaining a stale DHCP assigned IP address after roaming to a different access point, and having to run ipconfig /release; ipconfig /restore to get XP to grab a new IP address, you'll undestand how tenaciously XP wants to old onto IP addresses. That's not it's job, or IMHO a great idea, but I think MS does it in self-defense.
This is correct behavior for RARP. If the machine that previously owned an IP address is NOT present and accounted for when polled, the DHCP server expires the ARP cache entry (deletes the MAC address from the ARP table) and re-assigns the IP address. Think of it as a lease time of about 12 minutes to take care of reboots, but nothing else.
Incidentally, wireless ports are handled a bit differently due to roaming issues. For example, Orinoco AP-2000 and such access points will expire radios after only 5 minutes. One reason is that most AP's have a relatively small MAC address table. The cheapo AP's can handle perhaps 32 radios. AP-4000 perhaps 64. AP-1000 and AP-2000, I think are 254 (the maximum for a Class C netmask). Keeping these entries live for the typical 24 hr DHCP lease time is guaranteed to overflow the MAC address table in busy locations. In addition, you cannot roam between access points if an AP will not release your IP address. I have the various coffee shop AP's set to expire in 1 minute, which means that if you roam between local AP's, you've got perhaps 1 minute for the AP's to switch (thanks to the lack of a common roaming protocol).
If you really want a long term DHCP lease, I've been using Freesco:
Longer is not better for wireless.